Shock-induced damage beneath impact craters is studied in this work. Two representative terrestrial rocks, San Marcos granite and Bedford limestone, are chosen as test target. Impacts into the rock targets with different combinations of projectile material, size, impact angle, and impact velocity are carried out at cm scale in the laboratory.
\r\n\r\nShock-induced damage and fracturing would cause large-scale compressional wave velocity reduction in the recovered target beneath the impact crater. The shock-induced damage is measured by mapping the compressional wave velocity reduction in the recovered target. A cm scale nondestructive tomography technique is developed for this purpose. This technique is proved to be effective in mapping the damage in San Marcos granite, and the inverted velocity profile is in very good agreement with the result from dicing method and cut open directly.
\r\n\r\nBoth compressional velocity and attenuation are measured in three orthogonal directions on cubes prepared from one granite target impacted by a lead bullet at 1200 m/s. Anisotropy is observed from both results, but the attenuation seems to be a more useful parameter than acoustic velocity in studying orientation of cracks.
\r\n\r\nOur experiments indicate that the shock-induced damage is a function of impact conditions including projectile type and size, impact velocity, and target properties. Combined with other crater phenomena such as crater diameter, depth, ejecta, etc., shock-induced damage would be used as an important yet not well recognized constraint for impact history.
\r\n\r\nThe shock-induced damage is also calculated numerically to be compared with the experiments for a few representative shots. The Johnson-Holmquist strength and failure model, initially developed for ceramics, is applied to geological materials. Strength is a complicated function of pressure, strain, strain rate, and damage. The JH model, coupled with a crack softening model, is used to describe both the inelastic response of rocks in the compressive field near the impact source and the tensile failure in the far field. The model parameters are determined either from direct static measurements, or from indirect numerical adjustment. The agreement between the simulation and experiment is very encouraging.
", "doi": "10.7907/39ZE-SY71", "publication_date": "2006", "thesis_type": "phd", "thesis_year": "2006" }, { "id": "thesis:2300", "collection": "thesis", "collection_id": "2300", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05302003-174154", "primary_object_url": { "basename": "SNL_Thesis.pdf", "content": "final", "filesize": 3839672, "license": "other", "mime_type": "application/pdf", "url": "/2300/1/SNL_Thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "I. The Heterogeneities at the Core-Mantle and Inner-Core Boundaries from PKP Phases. II. The Static and Dynamic Behavior of Silica at High Pressures", "author": [ { "family_name": "Luo", "given_name": "Sheng-Nian", "clpid": "Luo-Sheng-Nian" } ], "thesis_advisor": [ { "family_name": "Clayton", "given_name": "Robert W.", "clpid": "Clayton-R-W" } ], "thesis_committee": [ { "family_name": "Clayton", "given_name": "Robert W.", "clpid": "Clayton-R-W" }, { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "clpid": "Ravichandran-G" }, { "family_name": "Asimow", "given_name": "Paul David", "clpid": "Asimow-P-D" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Waveform and differential travel-time (DTT) of various PKP phases have been utilized to study the velocity variations at the core-mantle boundary (CMB) and the inner-core boundary (ICB). The spatial concentration of events and stations, and the significant variations in PKPab-PKPdf DTT and waveform of PKPab, indicate localized sharp lateral variation of velocity at the CMB as supported by simulations. Modeling of DTT's among PKiKP, PKIKP and PKP-B-diffracted (Bdiff) phases, and waveform of Bdiff supports that the ratio of relative velocity variations of S- and P-wave at the CMB is larger than 2, and that hemispheric P-wave velocity variations exist at the top of the inner core, and that D' structure is related to the ICB via core dynamics.
\r\n\r\nThe equation of state of stishovite is obtained by direct shock wave loading up to 235 GPa as K0T=306 \u00b1 5 GPa and K0T' = 5.0 \u00b1 0.2 where K0T is ambient bulk modulus and K0T' its pressure derivative. Phase diagram of silica (including melting curve) up to megabar pressure regime is established based on molecular dynamics (MD) simulations and dynamic and static experiments. Calculations show that perovskite is thermodynamically stable relative to the stishovite and periclase assemblage at lower mantle conditions. A detailed and quantitative examination is conducted on the thermodynamics and phase change mechanisms (including amorphization) that occur upon shock wave loading and unloading of silica. The systematics of maximum undercooling and superheating, are established by incorporating normalized energy barrier for nucleation and heating (cooling) rate, and validated at the atomic level with systematic MD simulations. By considering superheating in shock wave experiments, high-pressure melting curves for silica, alkali halides and transition metals are constructed based on the Lindemann law and the $ln2$ rule for the entropy of melting.
", "doi": "10.7907/D8HB-A439", "publication_date": "2003", "thesis_type": "phd", "thesis_year": "2003" }, { "id": "thesis:4432", "collection": "thesis", "collection_id": "4432", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11072002-135150", "primary_object_url": { "basename": "Thesis.pdf", "content": "final", "filesize": 1523959, "license": "other", "mime_type": "application/pdf", "url": "/4432/9/Thesis.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Impact-Ionization Mass Spectrometry of Cosmic Dust", "author": [ { "family_name": "Austin", "given_name": "Daniel Ephraim", "clpid": "Austin-Daniel-Ephraim" } ], "thesis_advisor": [ { "family_name": "Beauchamp", "given_name": "Jesse L.", "clpid": "Beauchamp-J-L" } ], "thesis_committee": [ { "family_name": "Weitekamp", "given_name": "Daniel P.", "clpid": "Weitekamp-D-P" }, { "family_name": "Collier", "given_name": "C. Patrick", "clpid": "Collier-C-P" }, { "family_name": "Beauchamp", "given_name": "Jesse L.", "clpid": "Beauchamp-J-L" }, { "family_name": "Lewis", "given_name": "Nathan Saul", "clpid": "Lewis-N-S" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "In situ characterization of cosmic dust grains typically involves impact-ionization time-of-flight mass spectrometry. Considering the performance and limitations of previous instruments, I designed and tested a novel, compact time-of-flight mass spectrometer for cosmic dust analysis. The instrument, Dustbuster, incorporates a large target area with a reflectron, simultaneously optimizing mass resolution, particle detection, and ion collection. Dust particles hit the 65-cm\u00b2 target plate and are partially ionized by the impact. The resulting ions, with broad energy and angular distributions, are accelerated through the modified reflectron, focusing ions spatially and temporally to produce high-resolution spectra.
\r\n\r\nInitial performance tests of the Dustbuster used laser desorption ionization of embedded metal and mineral samples to simulate particle impacts. Mass resolution (mass/peakwidth) in these experiments ranged from 60 to 180, permitting resolution of isotopes. Subsequent experiments included hypervelocity microparticle impacts. Charged iron and copper microparticles, accelerated to 2-20 km/s in a 2 MV van de Graaff accelerator, impacted the Dustbuster. Mass resolution in these experiments ranged from 150 to 300 for iron and copper. Hydrogen, carbon, and oxygen ions appeared in many spectra. Field-induced emission of electrons immediately before impact is a possible cause of ion formation from species with high ionization potentials. The implications of this ionization effect are discussed in relation to interpretation of mass spectra from other in situ dust analyzers.
\r\n\r\nAnother time-of-flight instrument, originally designed as an energy analyzer, shows promise as a high-resolution mass spectrometer for high-flux cosmic dust environments.
\r\n\r\nIce is an important component of particulates ejected from comets and other icy bodies in the solar system. Due to limited experimental data on ice particle impacts, I built an ice particle source based on a vibrating orifice aerosol generator connected directly to vacuum. Ice particles produced in this manner can be electrostatically accelerated for impact ionization studies.
\r\n\r\nHypervelocity impact vaporization may have played a key role in the mass extinction that occurred at the Cretaceous-Tertiary (K-T) boundary. In order to study the speciation of gases that may have been produced in such an asteroid impact, I designed a specialized orthogonal extraction mass spectrometer for future laboratory impact experiments.
", "doi": "10.7907/2E8R-G492", "publication_date": "2003", "thesis_type": "phd", "thesis_year": "2003" }, { "id": "thesis:3744", "collection": "thesis", "collection_id": "3744", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09242008-095607", "type": "thesis", "title": "Collisional Processes Involving Icy Bodies in the Solar System", "author": [ { "family_name": "Stewart", "given_name": "Sarah Toby", "orcid": "0000-0001-9606-1593", "clpid": "Stewart-Sarah-Toby" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" } ], "thesis_committee": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Brown", "given_name": "Michael E.", "orcid": "0000-0002-8255-0545", "clpid": "Brown-M-E" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-W-B" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "1. The Shock Hugoniot of Solid Ice:
\r\n\r\nWe present a complete description of the solid ice Hugoniot based on new shock wave experiments conducted at an initial temperature of 100 K and previously published data obtained at 263 K. We identify five regions on the solid ice Hugoniot: (1) elastic shock waves, (2) ice Ih deformation shocks, transformation shocks to (3) ice VI, (4) ice VII, and (5) liquid water. In each region, data obtained at different initial temperatures are described by a single Us - Δup shock equation of state. The dynamic strength of ice Ih is strongly dependent on temperature. The Hugoniot Elastic Limit varies from 0.05 to 0.62 GPa, as a function of temperature and peak shock stress. We estimate the entropy and temperature along the 100 and 263 K Hugoniots and derive the critical pressures for shock-induced incipient (IM) and complete (CM) melting upon release. On the 100 K Hugoniot, the critical pressures are about 4.5 and between 5-6 GPa for IM and CM, respectively. On the 263 K Hugoniot, the critical pressures are 0.6 and 3.7 GPa for IM and CM, lower than previously suggested. Shock-induced melting of ice will be widespread in impact events.
\r\n\r\n2. Rampart Crater Formation on Mars:
\r\n\r\nWe present a model for the fluidization of Martian rampart crater ejecta blankets with liquid water based on the shock physics of cratering onto an ice-rich regolith. We conducted simulations of crater formation on Mars, explicitly accounting for the equations of state and shock-induced melting criteria for both the silicate and ice components and using strength models constrained by the observed transition diameter DTr from simple to complex craters on Mars, where DTr = 8 km corresponds to an effective yield strength of 107 Pa.
\r\n\r\nFor the observed size range of rampart craters (diameters D ≾ 30 km) and typical asteroidal impact conditions (silicate impactors, D ≾ 1 km, at 10 km s-1), we find that the hemispherical volume where subsurface ice is partially melted by the impact shock has a radius of about 15 projectile radii (rp), much larger than previous predictions of about 6 rp. The radius of the final crater is comparable to the radius of partial melting and more than half the ice within the excavated material is melted. Thus, the amount of shock-melted water incorporated into the continuous ejecta blanket is within a factor of two of the near-surface ground ice content.
\r\n\r\nWe find that fluidized ejecta blankets may form in the current climate with mean surface temperatures of 200 K. Decreasing the effective yield strength of the modeled materials, e.g., by increasing the ice content or porosity, modifies the impact-induced flow in the excavated cavity, resulting in deeper projectile penetration, steeper ejection angles, higher crater rim uplift, and reduced final crater diameter. The volume fraction of shock-melted water in the ejecta blanket increases with distance from the crater rim. The horizontal flow velocities during emplacement of fluidized ejecta (~ 10 - 1000 m s-1) is nearly constant in the continuous ejecta blanket and within the range of large terrestrial landslides. Therefore, ground-hugging debris flow conditions are achieved. The ejecta blanket properties from impacts into a Martian regolith containing 20-40%vol near-surface ice are consistent with the fraction of liquid water inferred from models of ejecta flow rheologies which produce rampart morphologies, about 10-30% liquid water by volume [Ivanov, B. A., Solar System Research, 30, 43-58, 1996].
\r\n\r\nWe present a model for the formation of different rampart ejecta morphologies which may be used in conjunction with an ejecta blanket debris flow model to map the distribution of ground ice. In addition, we find that formation of single or multiple-rampart ejecta blankets does not require pre-existing liquid water in the Martian crust. We estimate the minimum water content in observed rampart ejecta blankets to be equivalent to a global layer of water 0.6 m thick. Based on the crater sampling efficiency, the implied global Martian ice content, within the upper 2 km of the crust, is equivalent to a global layer of water 100 m deep. This result is comparable to other estimates of HM2O content in the Martian crust.
\r\n", "doi": "10.7907/0V4Q-VF61", "publication_date": "2002", "thesis_type": "phd", "thesis_year": "2002" }, { "id": "thesis:8168", "collection": "thesis", "collection_id": "8168", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03252014-144322918", "primary_object_url": { "basename": "Ni_s_2001.pdf", "content": "final", "filesize": 28950625, "license": "other", "mime_type": "application/pdf", "url": "/8168/1/Ni_s_2001.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "2D Modeling of Lower Mantle Structure with WKM Synthetics", "author": [ { "family_name": "Ni", "given_name": "Sidao", "orcid": "0000-0003-2988-4850", "clpid": "Ni-Sidao" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Gurnis", "given_name": "Michael C.", "orcid": "0000-0003-1704-597X", "clpid": "Gurnis-M-C" }, { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" }, { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The Earth is very heterogeneous, especially in the region close to the surface of the\r\nEarth, and in regions close to the core-mantle boundary (CMB). The lowermost\r\nmantle (bottom 300km of the mantle) is the place for fast anomaly (3% faster S\r\nvelocity than PREM, modeled from Scd), for slow anomaly (-3% slower S velocity than\r\nPREM, modeled from S,ScS), for extreme anomalous structure (ultra-low velocity\r\nzone, 30% lower inS velocity, 10% lower in P velocity). Strong anomaly with larger\r\ndimension is also observed beneath Africa and Pacific, originally modeled from travel\r\ntime of S, SKS and ScS. Given the heterogeneous nature of the earth, more accurate\r\napproach (than travel time) has to be applied to study the details of various anomalous\r\nstructures, and matching waveform with synthetic seismograms has proven effective\r\nin constraining the velocity structures. However, it is difficult to make synthetic\r\nseismograms in more than 1D cases where no exact analytical solution is possible.\r\nNumerical methods like finite difference or finite elements are too time consuming\r\nin modeling body waveforms. We developed a 2D synthetic algorithm, which is\r\nextended from 1D generalized ray theory (GRT), to make synthetic seismograms\r\nefficiently (each seismogram per minutes). This 2D algorithm is related to WKB\r\napproximation, but is based on different principles, it is thus named to be WKM, i.e.,\r\nWKB modified. WKM has been applied to study the variation of fast D\" structure\r\nbeneath the Caribbean sea, to study the plume beneath Africa. WKM is also applied\r\nto study PKP precursors which is a very important seismic phase in modeling lower\r\nmantle heterogeneity. By matching WKM synthetic seismograms with various data,\r\nwe discovered and confirmed that (a) The D\" beneath Caribbean varies laterally, and\r\nthe variation is best revealed with Scd+Sab beyond 88 degree where Sed overruns\r\nSab. (b) The low velocity structure beneath Africa is about 1500 km in height, at\r\nleast 1000km in width, and features 3% reduced S velocity. The low velocity structure\r\nis a combination of a relatively thin, low velocity layer (200 km thick or less) beneath\r\nthe Atlantic, then rising very sharply into mid mantle towards Africa. (c) At the\r\nedges of this huge Africa low velocity structures, ULVZs are found by modeling the\r\nlarge separation between S and ScS beyond 100 degree. The ULVZ to the eastern\r\nboundary was discovered with SKPdS data, and later is confirmed by PKP precursor\r\ndata. This is the first time that ULVZ is verified with distinct seismic phase.", "doi": "10.7907/J8XC-TF53", "publication_date": "2001", "thesis_type": "phd", "thesis_year": "2001" }, { "id": "thesis:16202", "collection": "thesis", "collection_id": "16202", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10062023-181634008", "primary_object_url": { "basename": "Holland_KG_1997.pdf", "content": "final", "filesize": 30615462, "license": "other", "mime_type": "application/pdf", "url": "/16202/1/Holland_KG_1997.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Phase Changes and Transport Properties of Geophysical Materials Under Shock Loading", "author": [ { "family_name": "Holland", "given_name": "Kathleen Gabrielle", "clpid": "Holland-Kathleen-Gabrielle" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Stock", "given_name": "Joann M.", "orcid": "0000-0003-4816-7865", "clpid": "Stock-J-M" } ], "thesis_committee": [ { "family_name": "Stock", "given_name": "Joann M.", "orcid": "0000-0003-4816-7865", "clpid": "Stock-J-M" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Wyllie", "given_name": "Peter J.", "clpid": "Wyllie-P-J" }, { "family_name": "Gurnis", "given_name": "Michael C.", "orcid": "0000-0003-1704-597X", "clpid": "Gurnis-M-C" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The lower mantle of the Earth is believed to be largely composed of (Mg, Fe)O (magnesiowiistite) and (Mg,Fe)SiO\u2083 (perovskite); thus the high pressure phase of (Mg,Fe)\u2082SiO\u2084 (olivine), which is believed to be perovskite plus magnesiowiistite is of geophysical interest. Radiative temperatures of single-crystal olivine starting material [(Mg_(0.9), Fe_(0.1))\u2082SiO\u2084] decreased abruptly from 7040 \u00b1 315 to 4300 \u00b1 270 K upon shock compression above 80 GPa. The data indicate that an upper bound to the solidus of the magnesiowiistite and perovskite assemblage at 4300 \u00b1 270 K is 130 \u00b1 3 GPa. These conditions correspond to those for partial melting at the base of the mantle, as has been suggested to occur within the recently discovered ultra-low-velocity zone (ULVZ) beneath the Central Pacific. We construct speculative high pressure phase diagrams for the MgO - SiO\u2082 system using experimental data from our work, and other mineral physics experiments.
\r\n\r\nIn separate experiments, time dependent shock temperatures were measured for stainless steel (SS) films sandwiched between two transparent Al\u2082O\u2083 anvils. The anvil material was the same as the driver material so that there would be symmetric heat flow from the sample. Inferred Hugoniot temperatures, T_h, of 5000 - 8500\u00b1500 Kat 222- 321 GPa are consistent with previous measurements in SS. Temperatures at the film\u00ad anvil interface (T_i), which are directly measured (rather than T_h) indicate that T_i did not decrease measurably during the approximately 250 ns that the shock wave took to traverse the Al\u2082O\u2083 anvil. Thus an upper bound is obtained for the thermal diffusivity of Al\u2082O\u2083 at the metal/anvil interface of K \u2264 14 \u00b1 5 cm\u00b2/s at 208 GPa and 2110 K. This is a factor of 1.6 lower than previously calculated values, resulting in a decrease of the inferred T_h by at least 400 K. The observed shock temperatures are combined with temperatures calculated from measured Hugoniots and are used to calculate the thermal conductivity of Al\u2082O\u2083. There was no measurable radiant-intensity decrease during the time when the shock wave propagated through the anvil; we infer from this that Al\u2082O\u2083 remained transparent while in the shocked state. Thus an Al\u2082O\u2083 anvil is sufficiently transparent for shock temperature measurements for metals, to at least 240 GPa.
\r\n\r\nFinally, shock temperature experiments employing a six-channel pyrometer were conducted on 200, 500, and 1000 \u00c5 thick films of Fe sandwiched between 3 mm thick anvils of Al\u2082O\u2083 and LiF, to measure the thermal diffusivity ratios of Al\u2082O\u2083/Fe and LiF/Fe, at high temperatures and pressures. Temperature decays of 3000 \u00b1 800 K in 250 ns were observed at Fe pressures of 194 - 303 GPa, which reflect the conduction of heat from the thin metal films into the anvil material. These results were achieved in experiments employing LiF anvils at 164 - 166 GPa and 4190 - 4220 K, and Al2O3 anvils at 196 - 303 GPa and 1410 - 2750 K. Thermal modeling of interface temperature versus time yields best fit thermal diffusivity ratios ranging from 15 \u00b1 30 to 80 \u00b1 20 (Fe/anvil) over the pressure and temperature range of the experiments. Calculated thermal conductivities for Fe, using electron gas theory, of 110 - 212 W /mK are used to calculate thermal conductivities for the anvil materials ranging from 6 to 12 W/mK. Debye theory predicts higher values of 8 to 34 W/mK. Data from previous experiments on thick (\u2265 100\u00b5m) films of Fe and stainless steel are combined with our present results from experiments on thin (\u2264 1000 \u00c5) films to infer a 5860 \u00b1 390 K Hugoniot temperature for the onset of melting of iron at 243 GPa. Our results address the question of whether radiation observed in shock temperature experiments on metals originates from the metal at the metal/ anvil interface or from the shocked anvil. We conclude that the photon flux from the shocked iron/anvil sandwich recorded in all experiments originates from the metal. Within the uncertainties of the shock temperature data, the uncertainties in shock temperatures resulting from the radiation from the anvils is negligible. This is in direct disagreement with previous conclusions of Kondo.
", "doi": "10.7907/cbd3-mk54", "publication_date": "1999", "thesis_type": "phd", "thesis_year": "1999" }, { "id": "thesis:775", "collection": "thesis", "collection_id": "775", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-02262008-153435", "type": "thesis", "title": "Impact-Induced Phase Transformations in Elastic Solids: A Continuum Study Including Numerical Simulations for GeO\u2082", "author": [ { "family_name": "Winfree", "given_name": "Nancy A.", "clpid": "Winfree-Nancy-A" } ], "thesis_advisor": [ { "family_name": "Knowles", "given_name": "James K.", "clpid": "Knowles-J-K" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "thesis_committee": [ { "family_name": "Knowles", "given_name": "James K.", "clpid": "Knowles-J-K" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "This thesis applies recently developed continuum theories of diffusionless phase transformations in solids to the study of impact problems involving materials which can experience such phase changes. Our objective is to compare the theoretical predictions against certain experimental results.
\r\n\r\nIn the experiments of interest, a face-to-face impact occurs between a disk of amorphous germanium dioxide and another material, either tungsten or an aluminum alloy. The GeO\u2082 is believed to transform to another phase if sufficient compressive stress is achieved.
\r\n\r\nWe model these experiments using one-dimensional finite elasticity. Phase-changing materials are represented by non-convex potential energy functions. This can produce phase boundaries that propagate subsonically or supersonically with respect to the slower longitudinal wave speed of the two phases. When a subsonic phase boundary is possible, it is not uniquely determined by the fundamental field equations and jump conditions. Uniqueness is obtained by invoking a nucleation criterion to control the initiation of the new phase, and a kinetic relation to govern its evolution.
\r\n\r\nThe experiments considered here are sufficiently long in duration (\u2248 3 \u00b5s) that several reflections and wave interactions occur, and the analysis becomes analytically intractable. Accordingly, a finite-difference method of Godunov type is employed to analyze these experiments numerically. Methods of Godunov type treat adjoining discretized spatial elements as the two sides of a Riemann problem, which is typically solved approximately by linearizing around the initial conditions on each side. Fortuitously, all constitutive models employed in this thesis are such that the required Riemann problems can be solved exactly without too much effort.
\r\n\r\nSimulations utilizing the numerical method demonstrate that the impact response of a material is sensitive to the kinetic relation that enters the model. It appears the theory may offer a plausible description of the experiments, though the restrictions placed on the constitutive models herein seem too severe to provide a good quantitative match to the experimental results.
", "doi": "10.7907/4dhf-fj83", "publication_date": "1999", "thesis_type": "phd", "thesis_year": "1999" }, { "id": "thesis:7626", "collection": "thesis", "collection_id": "7626", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04232013-084302487", "type": "thesis", "title": "I. Rigid Body Penetration into Brittle Material. II. Phase Change Effect on Shock Wave Propagation", "author": [ { "family_name": "Liu", "given_name": "Cangli", "clpid": "Liu-Cangli" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Stock", "given_name": "Joann M.", "orcid": "0000-0003-4816-7865", "clpid": "Stock-J-M" } ], "thesis_committee": [ { "family_name": "Stock", "given_name": "Joann M.", "orcid": "0000-0003-4816-7865", "clpid": "Stock-J-M" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Clayton", "given_name": "Robert W.", "orcid": "0000-0003-3323-3508", "clpid": "Clayton-R-W" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" }, { "family_name": "Ustundag", "given_name": "Ersan", "clpid": "Ustundag-E" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Part I.
\r\n\r\nWe have developed a technique for measuring the depth time history of rigid body penetration into brittle materials (hard rocks and concretes) under a deceleration of ~ 105 g. The technique includes bar-coded projectile, sabot-projectile separation,\r\ndetection and recording systems. Because the technique can give very dense data on penetration depth time history, penetration velocity can be deduced. Error analysis shows that the technique has a small intrinsic error of ~ 3-4 % in time during penetration, and 0.3 to 0.7 mm in penetration depth. A series of 4140 steel projectile penetration into G-mixture mortar targets have been conducted using the Caltech 40 mm gas/ powder gun in the velocity range of 100 to 500 m/s.
\r\n\r\nWe report, for the first time, the whole depth-time history of rigid body penetration into brittle materials (the G-mixture mortar) under 105 g deceleration. Based on the experimental results, including penetration depth time history, damage of recovered target and projectile materials and theoretical analysis, we find:
\r\n\r\n1. Target materials are damaged via compacting in the region in front of a projectile and via brittle radial and lateral crack propagation in the region surrounding the penetration path. The results suggest that expected cracks in front of penetrators may be stopped by a comminuted region that is induced by wave propagation. Aggregate erosion on the projectile lateral surface is < 20% of the final penetration depth. This result suggests that the effect of lateral friction on the penetration process can be ignored.
\r\n\r\n2. Final penetration depth, Pmax, is linearly scaled with initial projectile energy per unit cross-section area, es , when targets are intact after impact. Based on the experimental data on the mortar targets, the relation is Pmax(mm) 1.15es (J/mm2 ) + 16.39.
\r\n\r\n3. Estimation of the energy needed to create an unit penetration volume suggests that the average pressure acting on the target material during penetration is ~ 10 to 20 times higher than the unconfined strength of target materials under quasi-static loading, and 3 to 4 times higher than the possible highest pressure due to friction and material strength and its rate dependence. In addition, the\r\nexperimental data show that the interaction between cracks and the target free surface significantly affects the penetration process.
\r\n\r\n4. Based on the fact that the penetration duration, tmax, increases slowly with es and does not depend on projectile radius approximately, the dependence of tmax on projectile length is suggested to be described by tmax(\u03bcs) = 2.08es (J/mm2 + 349.0 x m/(\u03c0R2), in which m is the projectile mass in grams and R is the projectile radius in mm. The prediction from this relation is in reasonable agreement with the experimental data for different projectile lengths.
\r\n\r\n5. Deduced penetration velocity time histories suggest that whole penetration history is divided into three stages: (1) An initial stage in which the projectile velocity change is small due to very small contact area between the projectile and target materials; (2) A steady penetration stage in which projectile velocity continues to decrease smoothly; (3) A penetration stop stage in which projectile deceleration jumps up when velocities are close to a critical value of ~ 35 m/s.
\r\n\r\n6. Deduced averaged deceleration, a, in the steady penetration stage for projectiles with same dimensions is found to be a(g) = 192.4v + 1.89 x 104, where v is initial projectile velocity in m/s. The average pressure acting on target materials during penetration is estimated to be very comparable to shock wave pressure.
\r\n\r\n7. A similarity of penetration process is found to be described by a relation between normalized penetration depth, P/Pmax, and normalized penetration time, t/tmax, as P/Pmax = f(t/tmax, where f is a function of t/tmax. After f(t/tmax is determined using experimental data for projectiles with 150 mm length, the penetration depth time history for projectiles with 100 mm length predicted by this relation is in good agreement with experimental data. This similarity also predicts that average deceleration increases with decreasing projectile length, that is verified by the experimental data.
\r\n\r\n8. Based on the penetration process analysis and the present data, a first principle model for rigid body penetration is suggested. The model incorporates the models for contact area between projectile and target materials, friction coefficient, penetration stop criterion, and normal stress on the projectile surface. The most important assumptions used in the model are: (1) The penetration process can be treated as a series of impact events, therefore, pressure normal to projectile surface is estimated using the Hugoniot relation of target material; (2) The necessary condition for penetration is that the pressure acting on target materials is not lower than the Hugoniot elastic limit; (3) The friction force on projectile lateral surface can be ignored due to cavitation during penetration. All the parameters involved in the model are determined based on independent experimental data. The penetration depth time histories predicted from the model are in good agreement with the experimental data.
\r\n\r\n9. Based on planar impact and previous quasi-static experimental data, the strain rate dependence of the mortar compressive strength is described by \u03c3f/\u03c30f = exp(0.0905(log(\u03ad/\u03ad_0) 1.14, in the strain rate range of 10-7/s to 103/s (\u03c30f and \u03ad are reference compressive strength and strain rate, respectively). The non-dispersive\r\nHugoniot elastic wave in the G-mixture has an amplitude of ~ 0.14 GPa and a velocity of ~ 4.3 km/s.
\r\n\r\nPart II.
\r\n\r\nStress wave profiles in vitreous GeO2 were measured using piezoresistance gauges in the pressure range of 5 to 18 GPa under planar plate and spherical projectile impact. Experimental data show that the response of vitreous GeO2 to planar shock loading\r\ncan be divided into three stages: (1) A ramp elastic precursor has peak amplitude of 4 GPa and peak particle velocity of 333 m/s. Wave velocity decreases from initial longitudinal elastic wave velocity of 3.5 km/s to 2.9 km/s at 4 GPa; (2) A ramp wave with amplitude of 2.11 GPa follows the precursor when peak loading pressure is 8.4 GPa. Wave velocity drops to the value below bulk wave velocity in this stage; (3) A shock wave achieving final shock state forms when peak pressure is > 6 GPa. The Hugoniot relation is D = 0.917 + 1.711u (km/s) using present data and the data of Jackson and Ahrens [1979] when shock wave pressure is between 6 and 40 GPa for \u03c10 = 3.655 gj cm3 . Based on the present data, the phase change from 4-fold to 6-fold coordination of Ge+4 with O-2 in vitreous GeO2 occurs in the pressure range of 4 to 15 \u00b1 1 GPa under planar shock loading. Comparison of the shock loading data for\r\nfused SiO2 to that on vitreous GeO2 demonstrates that transformation to the rutile structure in both media are similar. The Hugoniots of vitreous GeO2 and fused SiO2 are found to coincide approximately if pressure in fused SiO2 is scaled by the ratio of fused SiO2to vitreous GeO2 density. This result, as well as the same structure, provides the basis for considering vitreous Ge02 as an analogous material to fused SiO2 under shock loading. Experimental results from the spherical projectile impact demonstrate: (1) The supported elastic shock in fused SiO2 decays less rapidly than a linear elastic wave when elastic wave stress amplitude is higher than 4 GPa. The supported elastic shock in vitreous GeO2 decays faster than a linear elastic wave; (2) In vitreous GeO2 , unsupported shock waves decays with peak pressure in the phase transition range (4-15 GPa) with propagation distance, x, as \u03b1 1/x-3.35 , close to the prediction of Chen et al. [1998]. Based on a simple analysis on spherical wave propagation, we find that the different decay rates of a spherical elastic wave in fused SiO2 and vitreous GeO2 is predictable on the base of the compressibility variation with stress under one-dimensional strain condition in the two materials.
\r\n\r\n", "doi": "10.7907/w8gc-n615", "publication_date": "1999", "thesis_type": "phd", "thesis_year": "1999" }, { "id": "thesis:5932", "collection": "thesis", "collection_id": "5932", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06072010-160325894", "primary_object_url": { "basename": "Zajac_bj_1998.pdf", "content": "final", "filesize": 13435545, "license": "other", "mime_type": "application/pdf", "url": "/5932/1/Zajac_bj_1998.pdf", "version": "v8.0.0" }, "type": "thesis", "title": "The State of Stress as Inferred from Deviated Boreholes: Constraints on the Tectonics of Offshore Central California and Cook Inlet, Alaska", "author": [ { "family_name": "Zajac", "given_name": "Blair J.", "clpid": "Zajac-Blair-J" } ], "thesis_advisor": [ { "family_name": "Stock", "given_name": "Joann M.", "orcid": "0000-0003-4816-7865", "clpid": "Stock-J-M" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Clayton", "given_name": "Robert W.", "orcid": "0000-0003-3323-3508", "clpid": "Clayton-R-W" }, { "family_name": "Gurnis", "given_name": "Michael C.", "orcid": "0000-0003-1704-597X", "clpid": "Gurnis-M-C" }, { "family_name": "Saleeby", "given_name": "Jason B.", "clpid": "Saleeby-J-B" }, { "family_name": "Stock", "given_name": "Joann M.", "orcid": "0000-0003-4816-7865", "clpid": "Stock-J-M" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This thesis introduces a new method of constraining the vector directions of the three principal stresses and their relative magnitudes, by using borehole breakouts in non-vertical drill holes. Unlike older stress state measurements from breakouts, this work does not presume that one of the principal stresses is Vertical. This method has important uses in complicated three-dimensional structures, such as in the Los Angeles basin, and in oil drilling applications.
\r\n\r\nChapter 1 discusses why knowledge of the three-dimensional stress tensor is relevant to today's science and examines the applications of the stress state determination technique discussed herein. The history of previous work is also described.
\r\n\r\nIn Chapter 2 I discuss the techniques of determining the stress tensor from borehole breakouts, examining the physics of borehole breakouts, the theory of the inversion technique used, and data processing issues. The theory and data processing issues are not discussed separately in this work, since data processing issues often prompted new theoretical techniques. I first examine the physics of borehole breakouts and how the orientation of breakouts on the borehole wall relates to the local stress field. A new borehole breakout selection scheme which takes into account highly non-vertical boreholes is then presented along with a discussion of the real world problems of data gathering, identification, and processing. Having selected a borehole breakout data set using the criteria, I invert for the best fitting stress state using a new technique combining genetic algorithms and non- differential function optimizers. Finally, I present a way in which 95% confidence limits can be placed on the resulting stress tensor.
\r\n\r\nWith all of the technical and theoretical pieces in place, I now examine several different data sets. Chapter 3 examines a borehole breakout data set publish by Qian and Pedersen [1991] from the Siljan Deep Drilling Project in Sweden and demonstrates that even for simple borehole breakout data sets, the stress state inversions assuming a vertical principal stress direction may fall outside of the 95% confidence limits of an inversion allowing non-vertical principal stress directions. My technique of displaying the borehole breakout data makes the data quality more obvious as compared to the way Qian and Pedersen [1991] plotted the data.
\r\n\r\nChapter 4 examines a borehole breakout data set from the offshore Santa Maria Basin, California. This analysis presents vertical borehole breakout data that represent a maximum horizontal principal stress direction of N7\u00b0E, roughly consistent with other earthquake focal mechanism, GPS, and borehole breakout studies in the area. However, the stress state inversion of breakouts identified in the vertical and a limited number of nearly horizontal boreholes suggests a stress state very different from any other stress state results. This could imply that the three dimensional stress in the Santa Maria Basin is very complicated. However, given the limited amount of borehole breakouts identified in nearly horizontal wells, the stress state results from this data set are inconclusive.
\r\n\r\nChapter 5 examines the largest data set used in this study, from a series of oil wells in Cook Inlet, Alaska. These are borehole caliper arm data from 21 different wells reaching a maximum deviation of 54\u00b0 and 3,223 m true vertical depth. Stress state inversions of 31 different subsets of the borehole breakout data were performed. Inversion of breakouts identified in the top two of three marker beds analyzed in wells drilled from the Baker platform identified nearly degenerate thrust faulting stress states with the maximum principal stress axis, S_1, oriented horizontally WNWESE, perpendicular to the NNE-trending anticlinal structures. The stress state from the deepest marker is also a nearly degenerate thrust faulting stress state with S_1 oriented NNW\u2014SSE, aligned with the regional direction of relative plate motion between the North American and Pacific plates. In between the shallow and deep stress state is an apparent normal faulting stress state with S_2 oriented subhorizontally ENE\u2014WSW. This clockwise rotation of the stress tensor as a function of depth suggests that the stress field changes with depth, from a shallow stress state responsible for the local NNE-trending structures to a deeper one from the North American and Pacific plates' collision zone. The observed normal faulting stress state between the two thrust faulting stress states is anomalous and may represent some sort of transition from the shallow to the deep stress state. Stress state profiles in 500 m true vertical depth (TVD) intervals show consistently oriented thrust faulting stress regimes with NNW\u2014SSE trending S_1 azimuths. The thrust faulting S_3 principal stress direction is consistently within 30\u00b0 of vertical, suggesting that while the assumption of a purely vertical principal stress direction is not valid, the stress tensor does not significantly rotate away from the surface conditions that require a purely vertical stress tensor. The nearly degenerate thrust faulting stress states determined from the Granite Point and the 10.8 km distant Baker platform breakouts are nearly identical, implying that the technique of using deviated borehole breakouts to invert for the regional stress is valid. The orientations of the maximum horizontal stress determined from the Cook Inlet borehole breakouts are consistent with other stress indicators in south-central Alaska and consistent with the direction of relative plate motion between the North American Plate and the Pacific plate. The S_1 axis for the Cook Inlet field trends due south plunging 3\u00b0. The 95% confidence limits allow the S_1 azimuth to vary from N156\u00b0E to N195\u00b0E and the plunge to vary from 10\u00b0 to -4\u00b0. This stress state does not appear representative of the stress field for each subset of breakouts. The Granite Point S1 axis trends N19\u00b0W plunging 3\u00b0; the 95% confidence limits allow the azimuth to vary from N42\u00b0W to N7\u00b0E and the plunge to vary from 1\u00b0 to 6\u00b0. The Baker platform S_1 axis trends N170\u00b0E plunging 8\u00b0; the 95% confidence limits on S_1 allow its azimuth to vary from N139\u00b0E to N191\u00b0E and its plunge to vary from 1\u00b0 to 15\u00b0. Finally, the Dillon platform S_1 axis trends N69\u00b0W plunging 2\u00b0; the 95% confidence limits constrain the S_1 azimuth from N268\u00b0E to N324\u00b0E and the plunge from 8\u00b0 to -4\u00b0. The more westerly orientation of S_1 at the Dillon platform may be related to the local NNE-trending anticlinal structures in the Cook Inlet Basin.
\r\n\r\nChapter 6 concludes and summarized the results and conclusions from the thesis.
\r\n\r\nThe first appendix contains in minute detail some of the mathematics describing the boreholes, breakouts, and coordinate system rotations used to perform this work. The second appendix contains the individual discussion and plots of the raw dipmeter data from all of the Cook Inlet, Alaska wells.
", "doi": "10.7907/S3V0-3M43", "publication_date": "1998", "thesis_type": "phd", "thesis_year": "1998" }, { "id": "thesis:770", "collection": "thesis", "collection_id": "770", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-02262007-141751", "primary_object_url": { "basename": "Chen_g_1998.pdf", "content": "final", "filesize": 10120655, "license": "other", "mime_type": "application/pdf", "url": "/770/1/Chen_g_1998.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "I. High pressure melting of [gamma]-iron and the thermal profile in the Earth's core. II. High pressure, high temperature equation of state of fayalite (Fe2SiO4)", "author": [ { "family_name": "Chen", "given_name": "George (Guangqing)", "clpid": "Chen-G-G" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Burnett", "given_name": "Donald S.", "clpid": "Burnett-D-S" }, { "family_name": "Stolper", "given_name": "Edward M.", "clpid": "Stolper-E-M" }, { "family_name": "Knowles", "given_name": "James K.", "clpid": "Knowles-J-K" }, { "family_name": "Tombrello", "given_name": "Thomas A.", "clpid": "Tombrello-T-A" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nThe melting curve of [...]-iron in the pressure range of 100 to 300 GPa has been derived by computing Gibbs free energies at high pressures and high temperatures from thermodynamic and equations of state (EOS) data for the [...], [...] and liquid-phases. Our calculations indicate the melting curve of iron is very sensitive to the EOS of both the solid [...] and melt phase. Our best estimate of the EOS parameters for [...]-iron are: p0 = 8.775 \u00b1 0.012 Mg/m3, [...] = 205 \u00b1 4 GPa, [...] = 4.80 \u00b1 0.01 (referenced to 12 GPa and 300 K). The calculation favors the melting curve of Boehler [1993] or Saxena et al. [1993]. Shock-wave experiments on pure iron preheated to 1573 K were conducted in 17-73 GPa range. The shock-wave equation of state of [gamma]-iron at 1573 K initial temperature can be fit with [...] = 4.102(0.015) km/s + 1.610(0.014)[...] with [...] = 7.413 \u00b1 0.012 Mg/m3. [Gamma]-iron's bulk modulus and its pressure derivative are 124.7\u00b11.1 GPa and 5.44\u00b10.06 respectively.\n\nWe present new data for sound velocities in the [gamma]- and liquid-phases. In the [gamma]-phase, to a first approximation, the longitudinal sound velocity is linear with respect to density: Vp = -3.13(0.72) + 1.119(0.084) [...] (units for Vp and [...] are km/s and Mg/m3 respectively). Melting was observed in the highest pressure (about 70-73 GPa) experiments at a calculated shock temperature of about 2775 \u00b1 160 K. This result is consistent with our calculated [...]-iron melting curve which is close to those measured by Boehler [1993] and Saxena et al. [1993]. The liquid iron sound velocity data yield a Gruneisen parameter value for liquid iron of 1.63\u00b10.28 at 9.37\u00b10.02 Mg/m3 at 71.6 GPa. The quantity [...] from our data is 15.2\u00b12.6 Mg/m3, which is within the bounds of Brown and McQueen [1986] (13.3-19.6 Mg/m3). Based on upward pressure and temperature extrapolation of our melting curve of [gamma]-iron, the estimated inner core-outer core boundary temperature is 5500\u00b1400 K, the temperature at the core-mantle boundary on the outer core side is about 3930\u00b1630 K, and the thermal boundary layer at the core-mantle boundary has a temperature difference between 400 and 1400 K.\n\nThe shock-wave equation of state of initially solid (300 K) and molten (1573 K) fayalite (Fe2SiO4, Fa) are reported in the ranges 23 to 212 GPa and 5 to 47 GPa, respectively. The 300 K data appear to undergo a phase change in the 35-55 GPa range. The density of the high pressure phase (HPP) is consistent with a dense oxide mixture. Although the initially 300 K fayalite may melt along its Hugoniot, this is not explicitly detected. Fitting the HPP Hugoniot data in the shock velocity ([...])-particle velocity ([...]) plane yields:\n\n[...] = 4.375(0.027) Mg/m3, (1)\n\n[...] = 4.07(0.22) km/s + 1.43(0.06) [...], (2)\n\nwhere [...] is the initial density. The isentropic bulk modulus [...] = 72.4 \u00b1 8.0 GPa, and its pressure derivative [...] = 4.72\u00b10.24. \n\nThe 1573 K data set yields:\n \n[...] = 3.750(0.018) Mg/m3, (3)\n \n[...] = 2.63(0.02) km/s + 1.59(0.01) [...], (4)\n\nand [...] = 25.9 \u00b1 0.4 GPa, [...] = 5.36 \u00b1 0.04. The bulk modulus compares favorably with Agee [1992a]'s result (24.4 GPa), but the pressure derivative is quite different (10.1 from Agee [1992a]).\n\nAbove 50 GPa, the high pressure regime of the Hugoniot of the solid fayalite can be fit with oxide mixture models using stishovite and FeO (either LPP or HPP). The fayalitic liquid compression data above 40 GPa are well fit with ideal mixing of partial molar volumes of stishovite and FeO (LPP or HPP), in support of the hypothesis of Rigden et al. [1989].\n\nA model basalt incorporating the liquid fayalite data shows the neutral buoyancy zone of basic silicate melts of plausible terrestrial compositions is at about 250-400 km depth based on the PREM Earth model.\n", "doi": "10.7907/z7r2-xf47", "publication_date": "1998", "thesis_type": "phd", "thesis_year": "1998" }, { "id": "thesis:3190", "collection": "thesis", "collection_id": "3190", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08212009-144428", "primary_object_url": { "basename": "Yang_w_1996.pdf", "content": "final", "filesize": 5052137, "license": "other", "mime_type": "application/pdf", "url": "/3190/1/Yang_w_1996.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Impact volatilization of calcite and anhydrite and the effect on global climate from K/T impact crater at Chicxulub", "author": [ { "family_name": "Yang", "given_name": "Wenbo", "clpid": "Yang-Wenbo" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "abstract": "In geophysics and planetary science, it is important to understand the shock devolatilization process of minerals as these represent key elements in our understanding of the formation and evolution of atmosphere and ocean.\r\n\r\nShock vaporization experiments were carried out for porous (70% crystal density) anhydrite and porous (54% crystal density) up to 76 and 19 GPa, respectively. Velocity histories of aluminum-LiF window interface, which were driven by the vapor, were measured using velocity interferometer. Incipient and complete vaporization of CaSo4 and CaCO3 criteria have been obtained through thermodynamic calculations in which chemical dissociation or shock melting is taken into account. The incipient and complete vaporization pressures are 81\u00b17 and 155\u00b113 GPa for crystal anhydrite, and 27\u00b11 and 67\u00b16 GPa for porous anhydrite. For porous calcite, the incipient and complete vaporization pressure are 5.4\u00b11.9 and 14.6\u00b13.8 GPa, respectively. For crystal calcite, they are 54\u00b16 and 103\u00b112 GPa, respectively.\r\n\r\nOne-dimensional numerical simulation was used to simulate the measured velocity profiles. The vaporized products can be described by equation, P=(\u03b3-1)\u03c1E, where \u03b3 varied as pressure changes.\r\n\r\nUsing the new criteria, the amount of degassed carbon and sulfur have been estimated from Chicxulub impact and their effects on the global temperature have been calculated and discussed. The global warming caused by the degassed CO2 is 0.2-1.1\u00b0C and the degassed SO2 may caused a global cooling of is 8.5-16\u00b0C.\r\n\r\nShock temperature measurements place constraints on high-pressure equation-of-states, permit detection and quantification of phase transformations.\r\n\r\nA high-sensitivity (24 mv/\u00b5W @850nm ), time-resolved six-channel pyrometer has been designed and constructed and used in shock temperature measurements. Due to the high gain of the system, small mineral samples (~5 mm in diameter) can be used in shock temperature experiments. Thermal conductivities of LiF and Al2O3 were measured, for the first time, using this new system, their values are 2-3 orders of magnitude less than theoretical values.\r\n", "doi": "10.7907/n3xq-qe28", "publication_date": "1996", "thesis_type": "phd", "thesis_year": "1996" }, { "id": "thesis:4379", "collection": "thesis", "collection_id": "4379", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11032003-101839", "primary_object_url": { "basename": "Chen_w_1995.pdf", "content": "final", "filesize": 14729328, "license": "other", "mime_type": "application/pdf", "url": "/4379/1/Chen_w_1995.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Dynamic failure behavior of ceramics under multiaxial compression", "author": [ { "family_name": "Chen", "given_name": "Weinong", "clpid": "Chen-Weinong" } ], "thesis_advisor": [ { "family_name": "Ravichandran", "given_name": "Guruswami", "clpid": "Ravichandran-G" } ], "thesis_committee": [ { "family_name": "Ravichandran", "given_name": "Guruswami", "clpid": "Ravichandran-G" }, { "family_name": "Rosakis", "given_name": "Ares J.", "clpid": "Rosakis-A-J" }, { "family_name": "Knowles", "given_name": "James K.", "clpid": "Knowles-J-K" }, { "family_name": "Ortiz", "given_name": "Michael", "clpid": "Ortiz-M" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "abstract": "An experimental technique has been developed that is capable of (1) dynamically loading the specimen in multiaxial compression; (2) controlling the stress state in the specimen in the range from uniaxial stress to uniaxial strain; and (3) allowing the recovery of the sample after loaded by a single, well defined pulse for the characterization of the failure mode. In this technique, cylindrical ceramic specimens were loaded in the axial direction using a split Hopkinson pressure bar modified to apply a single loading pulse, and were confined laterally either by shrink fit sleeves, or by eletro-magnetic force.\r\n\r\nQuasi-static and dynamic multiaxial compression experiments have been performed on a machinable glass ceramic, Macor, and a monolithic engineering ceramic, sintered aluminum nitride (A1N). The cylindrical ceramic specimens were confned laterally by shrink fit sleeves: the amount of confining pressure (0-230 MPa) was varied by using different sleeve materials. The quasi-static axial load was applied by a hydraulic driven Material Test System (MTS), whereas the dynamic axial load was provided by a modified split Hopkinson (Kolsky) pressure bar (SHPB). Under both quasi-static and dynamic loading conditions, the experimental results for both materials showed that the failure mode changed from fragmentation by axial splitting under conditions of uniaxial stress (without lateral confinement) to localized deformation on faults under moderate lateral confinement. The fault initiation process was studied experimentally in detail. Based on the experimental results, a compressive brittle failure process was summarized. A transition from brittle to ductile behavior was observed in Macor under high confinement pressure which was achieved using a second sleeve around the inner sleeve. The compressive failure strengths of both materials increased with increasing confinement pressure under both quasi-static and dynamic loading conditions. The highest dynamic compressive strengths of Macor and A1N measured in the experiments were 1.35 GPa and 5.40 GPa, respectively, whereas their quasi-static compressive strength were measured to be 0.43 GPa and 2.5 GPa, respectively.\r\n\r\nBased on the experimental results on A1N together with available data in the literature, a failure/flow criterion was developed for ceramic materials under multiaxial loading. A Mohr-Coulomb criterion and an improved Johnson-Holmquist model were found to fit the experimental data for brittle failure, whereas the materials exhibited pressure insensitive plastic flow at high pressures. Observations made in other types of dynamic experiments (e.g., shock wave loading) were rationalized based on the postulated failure mechanisms and the possibility of plastic flow beyond the Hugoniot elastic limit (HEL). The effect of various material properties on the failure behavior was investigated using the proposed failure criterion. The applicability of the present model to a range of ceramics was also explored and the limitations of the model were outlined.\r\n", "doi": "10.7907/0NNE-JD20", "publication_date": "1995", "thesis_type": "phd", "thesis_year": "1995" }, { "id": "thesis:4344", "collection": "thesis", "collection_id": "4344", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-10312007-090136", "type": "thesis", "title": "Three-Dimensional Seismic Velocity Structure of the Earth's Outermost Core and Mantle", "author": [ { "family_name": "Kohler", "given_name": "Monica Diane", "orcid": "0000-0002-4703-190X", "clpid": "Kohler-Monica-Diane" } ], "thesis_advisor": [ { "family_name": "Tanimoto", "given_name": "Toshiro", "clpid": "Tanimoto-T" }, { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" }, { "family_name": "Clayton", "given_name": "Robert W.", "clpid": "Clayton-R-W" }, { "family_name": "Kanamori", "given_name": "Hiroo", "clpid": "Kanamori-H" }, { "family_name": "Tanimoto", "given_name": "Toshiro", "clpid": "Tanimoto-T" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Obtaining an accurate, detailed picture of deep-Earth structure is of fundamental importance in a wide range of geophysical applications such as fluid dynamic, magnetohydrodynamic, and mineral physics models of the Earth which incorporate properties determined from seismology. Because it is such a drastic chemical and thermal boundary layer, the nature of the core-mantle boundary has important implications for deep-Earth processes, particularly those which have their origin in the lower mantle or outer core. Seismic data provide the most direct method of sampling the Earth's interior and are, therefore, useful for determining deep-Earth material properties.
\r\n\r\nThe goal of this work has been to present models of three-dimensional, shear and compressional velocity structure which are self-consistent with the data and which can be used in other geophysical applications. The numerical inversions consisted of determining the three-dimensional structure of the outermost core and mantle of the Earth from long-period seismic waveforms. This approach is distinct from other global models of deep-Earth heterogeneity because it accounts for possible lateral heterogeneity in an outermost core layer whose properties are constrained by seismic phases which travel through the core-mantle boundary region.
\r\n\r\nThis method is different from previous core studies in several important ways: synthetic seismograms are constructed using short-period normal modes for the entire set of body-wave phases which travel through the interior of the Earth (e.g., P, PP, S, SS, SKS). Over 5000 seismograms from global digital seismic networks were collected and processed. First-order perturbations in P-wave velocities in one outermost core layer and S-wave velocities within 11 mantle layers of varying thicknesses comprised the least-squares solutions to the inverse problem. Spheroidal modes with periods between 33 and 100 sec were selected to model the body-wave portion of seismograms recorded from earthquakes which occurred globally.
\r\n\r\nThe preferred model is a 12-layered model incorporating data weighted by inverse data variance. This model produces velocity anomalies in the mantle and outermost core which are acceptable for first-order perturbation methods. The results of one-layer inversions also point to the possible existence of lateral variations in the outermost core, most likely between \u00b10.5% but not as large as \u00b15%. This model suggests that outermost core P-wave velocity perturbations accompany S-wave velocity perturbations in the lowermost mantle to produce observed variations in SKS-S and SKKS-SKS travel times. In addition, the patterns of structure vary smoothly and exhibit both large and small scale features. The spectral amplitudes fall off more rapidly for the lower mantle layers than for the upper mantle. The depth resolution displayed by the c\u2070\u2080 spherical harmonic term is 200-300 km for upper mantle layer midpoints and increases to 500-600 km for lower mantle layer midpoints.
\r\n\r\nThe data variance reduction of entire body-wave portions as well as SnKS portions of seismograms are slightly better for the 12-layered model than for the 11-layered model; however, the total variance reductions were never very large. The results of the F ratio suggest that lateral velocity variations in the outermost core layer are not zero and that the deepest layer is statistically significant. This test does not require that the extra layer lie in the outermost core (as opposed to the lowermost mantle).
\r\n\r\nThe results of pattern retrieval resolution tests support the conclusion that structure of the outermost core has been obtained independently from the mantle. Multiplicative factors have been calculated from the resolution tests using synthetic Earth models to place constraints on the amount of power leakage suspected from one region to another due to incomplete data coverage. An upper bound of 84% and a lower bound of 68% of the power of outermost core structure is, in fact, due to heterogeneity in the outermost core. By the same analysis, less than 100% of the power of structure initially placed in the lowermost mantle was retrieved in that layer after the resolution inversion. An upper bound of 60% and a lower bound of 53% of the power of lowermost mantle structure is, in fact, due to D\" heterogeneity. Almost no leakage occurred from structure initially placed in the uppermost mantle layer.
\r\n\r\nSeveral possible sources of lateral velocity anomalies for the lowest layers are explored. Invoking thermal coupling between the mantle and core, one explanation is that the fluid surfaces are deformed due to cold downwellings of lower mantle, and as a result, outermost core fluid. This will give the appearance of lateral velocity anomalies. If lateral velocity anomalies indeed exist, they are likely to be due to a combination of lateral temperature variations and chemical inhomogeneity, suggested by mineral physics relationships.
\r\n", "doi": "10.7907/q3fd-fd26", "publication_date": "1995", "thesis_type": "phd", "thesis_year": "1995" }, { "id": "thesis:4375", "collection": "thesis", "collection_id": "4375", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11022007-110943", "primary_object_url": { "basename": "Gazis_ca_1995.pdf", "content": "final", "filesize": 57523337, "license": "other", "mime_type": "application/pdf", "url": "/4375/1/Gazis_ca_1995.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "An isotopic study of the fluid flow and thermal history of the 2.8 Ma Chegem ash-flow caldera and related intrusive rocks (Caucasus Mountains, Russia)", "author": [ { "family_name": "Gazis", "given_name": "Carey Alice", "clpid": "Gazis-C-A" } ], "thesis_advisor": [ { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" } ], "thesis_committee": [ { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" }, { "family_name": "Burnett", "given_name": "Donald S.", "clpid": "Burnett-D-S" }, { "family_name": "Stolper", "given_name": "Edward M.", "clpid": "Stolper-E-M" }, { "family_name": "Rossman", "given_name": "George Robert", "clpid": "Rossman-G-R" }, { "family_name": "Saleeby", "given_name": "Jason B.", "clpid": "Saleeby-J-B" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Epstein", "given_name": "Samuel", "clpid": "Epstein-S" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe 2.8 Ma Chegem caldera, an 11x15 km ash-flow caldera located in the Caucasus Mountains, presents a unique opportunity to study silicic magma systems because of its combination of youth, exposure and simplicity. Rapid uplift and erosion in the region has exposed over 2 km of flatlying caldera fill, consisting of densely welded tuff (rhyolitic to dacitic), overlain by glacial deposits and andesite flows and cut by a granodiorite porphyry intrusion. The Eldjurta Granite, whose age and composition are similar to the Chegem volcanics, is exposed in an adjacent river valley 10 km to the northeast. Major Mo-W deposits located in nearby skarns have prompted mineral-exploration drillholes (to 4 km depth) in the granite. An isotopic study of the rocks of the Chegem caldera and the Eldjurta Granite has been performed to examine their petrogenesis, fluid flow and thermal histories.\r\n\r\nBiotite and sanidine [...] ages for 8 Chegem Tuff samples and the granodiorite intrusion are analytically indistinguishable at 2.82 \u00b1 0.02 Ma. Thus, the Chegem Tuff was erupted, cooled and intruded by the granodiorite within < 50,000 yrs. In the nearby Eldjurta Granite, biotite and K-feldspar [...] ages for 11 samples, including 8 from the deep drillhole (to 3970m depth) yield ages between 0.83 \u00b1 0.29 Ma and 2.78 \u00b1 0.09 Ma. A decrease in biotite ages from 1.90 \u00b1 0.24 Ma near the roof of the granite to 0.83 \u00b1 0.29 Ma at 3970m depth, apparently records the uplift and cooling history of this pluton. The ages of the upper 10 samples imply an isotherm migration rate of 13 mm/yr, probably due to a combination of downward migration of isotherms and regional uplift.\r\n\r\nOxygen isotope studies of the intracaldera tuff, including 38 samples from a continuous 1405m-stratigraphic section, reveal a striking caldera-wide stratigraphic horizon of [...]-depleted rocks in which there is extreme disequilibrium between phenocrysts and groundmass (sometimes still glassy). All quartz and feldspar phenocrysts have \"normal\" igneous [...] values of [...]8.5 and [...]7.0, respectively. Whole-rock and groundmass [...] values are as low as -4.0 and -7.7, respectively. Infrared spectroscopic analyses of glassy pumices reveal that they contain 3.3 to 4.8 wt% water. The [...] and water speciation of these glasses reflects low-temperature hydration by meteoric water, whereas some of their [...] values require higher temperature water-glass interaction.\r\n\r\nPronounced disequilibrium between coexisting feldspar and groundmass or glass has never been observed before on this scale. It requires a hydrothermal event involving large amounts of low-[...] H2O at sufficiently high temperatures and short enough time that glass exchanges thoroughly but feldspar does not. The most likely process responsible for the [...] depletions at Chegem is a high-temperature (500-600\u00b0C), short-lived (10-25 years), vigorous meteoric-hydrothermal event similar to that which occurred at the Valley of Ten Thousand Smokes, Alaska. Mass balance calculations indicate fluid fluxes of [...] mol/[...]-sec over that time period. Sr isotopic studies reveal that this hydrothermal event caused increases in whole-rock [...], possibly because the hydrothermal waters attained radiogenic Sr from crystalline rocks which were incorporated in the caldera fill during caldera collapse.\r\n\r\n[...] ratios of unaltered Chegem volcanic and intrusive rocks range from 0.7044 to 0.7060, significantly lower than values for surrounding country rock (0.7070 to 0.7319). Thus, the Chegem magmas were probably derived from the mantle or lower crust. The [...] ratios correlate with major- and trace-element trends, indicating that the Chegem magma chamber was both isotopically and compositionally zoned. Compared to the Chegem rocks, the Eldjurta Granite has higher [...] (0.7069), [...] and [...], and so must have evolved separately at some time.\r\n", "doi": "10.7907/mjb1-6r66", "publication_date": "1995", "thesis_type": "phd", "thesis_year": "1995" }, { "id": "thesis:7397", "collection": "thesis", "collection_id": "7397", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01142013-104747074", "primary_object_url": { "basename": "Rowan_lr_1993.pdf", "content": "final", "filesize": 38194629, "license": "other", "mime_type": "application/pdf", "url": "/7397/1/Rowan_lr_1993.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Equation of state of molten mid-ocean ridge basalt. Structure of Kilauea volcano.", "author": [ { "family_name": "Rowan", "given_name": "Linda Rose", "clpid": "Rowan-L-R" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Stolper", "given_name": "Edward M.", "clpid": "Stolper-E-M" }, { "family_name": "Clayton", "given_name": "Robert W.", "clpid": "Clayton-R-W" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Stolper", "given_name": "Edward M.", "clpid": "Stolper-E-M" }, { "family_name": "Clayton", "given_name": "Robert W.", "clpid": "Clayton-R-W" }, { "family_name": "Rossman", "given_name": "George Robert", "clpid": "Rossman-G-R" }, { "family_name": "Westphal", "given_name": "James A.", "clpid": "Westphal-J-A" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Basalts are the most ubiquitous rocks erupting at the earth's surface at the present\r\ntime and they provide an important probe of the subsurface processes occurring\r\nwithin planetary interiors. Recent advances in both mineral physics and seismic\r\nanalysis have allowed me to undertake two independent studies related to the genesis\r\nand eruption of basaltic magmas. Chapters 1 and 2 are part of an experimental study\r\nconducted in the shock wave laboratory on the equation of state of molten mid-ocean\r\nridge basalt and the chemical interactions of the shocked liquid with its Mo container.\r\nMy advisors for this project were Thomas Ahrens and Edward Stolper. Chapter 3 is a\r\ntravel time tomography study of the three-dimensional structure of Kilauea Volcano,\r\nHawaii in collaboration with Robert Clayton. Chapter 3 is currently in press in the\r\nJournal of Geophysical Research.
\r\n\r\nThe EOS of molten MORB to 20 GPa was accomplished using the innovative silicate\r\nliquid shock wave measurement technique on the 40 mm propellant gun developed\r\nby Rigden [1986] and Miller [1990). This technique has been used to determine\r\nthe EOS for four synthetic melts and this thesis applies the technique to a natural\r\nmelt, a MORB dredged from the Juan de Fuca ridge. The resulting EOS indicates\r\nthat the MORB liquid is very compressible and therefore has a low bulk modulus of\r\n11.7 GPa. These results are consistent with low pressure static compression experiments\r\non similar basalts, but are not consistent with the results of ultrasonic interferometry.\r\nThe compressible nature of the MORB liquid is related to its composition\r\nand this may be expressed best by comparing the MORB Hugoniot to the Hugoniot\r\ndetermined for An_(36)Di_(64) and komatiite. The MORB and An_(36)Di_(64) Hugoniots show\r\nsignificant increase in density at low pressure followed by a stiffening at high pressures\r\nwhere the liquid Hugoniot approaches its respective dense oxide high pressure\r\ncomposition. This may be related to gradual coordination changes from four-fold to\r\nsix-fold for the Si^(+4) and Al^(+3) which are essentially complete at the high pressure\r\nwhere the curve stiffens. The MORB is much more compressible than the komatiite\r\nand overtakes the komatiite in density at a low pressure of 2.5 GPa. This is a\r\ncompositional effect caused by the enrichment of the MORB in Al_2O_3 and SiO_2 and\r\ndepletion in MgO compared to komatiite. The compressible nature of the MORB\r\nallows it to become denser than the surrounding mantle near the base of the low\r\nvelocity zone and therefore it is unlikely that MORB can be derived from very deep\r\nin the earth's upper mantle.
\r\n\r\nFor most shock wave experiments, the sample is not recovered and nothing can\r\nbe determined about its structure or composition due to the passage of the shock\r\nwave. In a few of my EOS experiments on molten MORB, however, the shocked sample\r\nwas recovered and could be studied in detail. Observations of impact-induced\r\ninteractions between the silicate liquid and its Mo container provide insight into\r\nplanetary impact and differentiation processes involving metal-silicate partitioning.\r\nThe shocked liquids showed extreme reduction and with increasing pressure the FeO\r\ncontent of the initial melt was reduced to almost nothing by reaction with the Mo.\r\nThese reactions produced metallic particles enriched in Mo, Fe and Si. These particles\r\nshow a similar texture as those found at impact sites on the earth and moon\r\nand provide clues to the impact origin of metallic particles.
\r\n\r\nA travel time tomography study of local P wave data from Kilauea Volcano,\r\nHawaii, was undertaken to determine the lateral heterogeneities produced by its intricate\r\nmagmatic and tectonic environment. The technique proved to be a powerful\r\nprobe of the volcano's intrusive plumbing because the presence of a dense seismic\r\narray and many local earthquakes allowed for excellent coverage of complex subsurface\r\nfeatures. Analysis and interpretation of the tomographic images leads to the\r\nfollowing inferrred model. The main shallow magma reservoir is delineated by a\r\nslow anomaly centered 2 km southeast of Halemaumau caldera. There is a distinct\r\nhigh velocity region centered northwest of the summit from 0 to 2 km depth that\r\nmay represent a dense wall and/or cap of intrusive rock that acts as a barrier or\r\ncontainment structure for the northern part of the reservoir. We suggest that the\r\nshallow reservoir is a narrow, compartmentalized region of sills and dikes because of\r\nthe closely spaced high and low velocity anomalies near the summit. The rift zones\r\nof Kilauea are imaged as major, high velocity entities, widening to the south with\r\ndepth until 6 km. These fast anomalies may be related to the sheeted dike complexes\r\nalong the rifts. On a finer scale, magma pockets centered at 0-2 km depth have been\r\ninferred beneath Makaopuhi, Mauna Ulu and Puu Oo, along the east rift zone. The\r\nHilina and Kaoiki fault zones, are imaged as slow features at shallow depths (less than 6\r\nkm), related to their tensional structures that produce the open fractures and cracks\r\nin the basaltic edifice. The Koae fault system is imaged as a slightly fast shallow\r\nstructure (less than 6 km) possibly related to intrusive diking from the adjacent rift zones.\r\nContinued inversions with the immense amount of seismic data collected for Hawaiian\r\nevents will allow the detailed development of a three-dimensional velocity model\r\nfor Kilauea. Such a model will be extremely useful to seismologists and petrologists\r\nalike for understanding the tectonic growth and magmatic evolution of this dynamic\r\nshield volcano.
\r\n\r\n", "doi": "10.7907/J6D0-GV56", "publication_date": "1993", "thesis_type": "phd", "thesis_year": "1993" }, { "id": "thesis:3176", "collection": "thesis", "collection_id": "3176", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08202007-130850", "primary_object_url": { "basename": "Rulison_aj_1992.pdf", "content": "final", "filesize": 7073251, "license": "other", "mime_type": "application/pdf", "url": "/3176/1/Rulison_aj_1992.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Part 1. Synthesis of ceramic powders by electrospray pyrolysis. Part 2. An approach to interplanetary particle sampling", "author": [ { "family_name": "Rulison", "given_name": "Aaron John", "clpid": "Rulison-A-J" } ], "thesis_advisor": [ { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" } ], "thesis_committee": [ { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nIn Part 1, the application of electrospray atomization for the production of ceramic powders is described. A model of the Taylor cone was developed which predicts the droplet size, volumetric flow rate, and electrical current for atomization of electrolytic solutions as functions of the liquid's specific electrical conductivity, surface tension, absolute viscosity, and density, as well as the applied electrical potential and atomizer geometry. Experimental verification was obtained for atomization of sodium iodide in n-propyl alcohol. The knowledge gleaned from the sodium iodide experiments was used to apply electrospray atomization to the production of submicron, spheroidal, and yttria particles by atomization of yttrium nitrate in n-propyl alcohol and thermal decomposition of the resulting aerosol droplets. This process is named \"electrospray pyrolysis.\" A means of increasing the ceramic powder production rate for industrial and more extensive laboratory use via arrays of Taylor cones was experimentally tested.\n\nIn Part 2, a method of sampling interplanetary dust particles (IDPs) is described. IDPs move at speeds [...]10 km/s relative to an interplanetary probe. A gas-filled balloon stops the particles by drag and ablation after they penetrate the balloon's skin. A model for ablation and deceleration of particles in the continuum and transition regimes was developed and experimentally tested using 7 [...] diameter glass spheres moving with an initial speed of 5 km/s through xenon gas at 0.1 and 0.2 atm. To analyze stopped IDPs by mass spectrometry, microscopy, etc., they must be deposited on a small sample substrate. To this end, a method of inward electrostatic precipitation was devised, modelled, and experimentally tested for [...] carbon soot particles in a cylindrical chamber. By this method, [...] IDPs can be intercepted by a [...] m noble gas-filled balloon, and deposited on a [...] mm centrally located sample substrate for subsequent analysis.", "doi": "10.7907/5tcw-c634", "publication_date": "1992", "thesis_type": "phd", "thesis_year": "1992" }, { "id": "thesis:2993", "collection": "thesis", "collection_id": "2993", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08012006-093137", "type": "thesis", "title": "I. Phase Transformations and the Spectral Reflectance of Solid Sulfur: Possible Metastable Sulfur Allotropes on Io's Surface. II. Photochemistry and Aerosol Formation in Neptune's Atmosphere", "author": [ { "family_name": "Moses", "given_name": "Julianne Ives", "orcid": "0000-0002-8837-0035", "clpid": "Moses-Julianne-Ives" } ], "thesis_advisor": [ { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" }, { "family_name": "Westphal", "given_name": "James A.", "clpid": "Westphal-J-A" } ], "thesis_committee": [ { "family_name": "Westphal", "given_name": "James A.", "clpid": "Westphal-J-A" }, { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "clpid": "Blake-G-A" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Burnett", "given_name": "Donald S.", "clpid": "Burnett-D-S" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This thesis consists of two independent papers:
\r\n\r\nPAPER I:
\r\n\r\nThe spectral reflectance of elemental sulfur is examined in a set of laboratory experiments to determine the factors that affect the transformation rate of monoclinic (\u03b2) sulfur and various other sulfur allotropes into orthorhombic (\u03b1) sulfur. The laboratory data have implications for the spectral variation and physical behavior of freshly solidified sulfur, if any exists, on Jupiter's satellite Io. Depending on its thermal history, molten sulfur on Io would initially solidify into a glassy solid or a monoclinic crystalline lattice; these forms might contain polymeric sulfur molecules as well as the more abundant S8 molecules. If freshly frozen sulfur on Io could lose heat rapidly and approach ambient dayside Io temperatures within several hours, then some of the metastable sulfur allotropes could be maintained on Io virtually indefinitely. Small droplets of sulfur ejected during plume eruptions might cool quickly enough to preserve these allotropes, but sulfur in large volcanic flows or lakes would probably remain warm long enough for phase transformations to proceed at a visible rate.
\r\n\r\nPAPER II:
\r\n\r\nPhotodissociation of methane at high levels in Neptune's atmosphere leads to the production of more complex hydrocarbon species such as ethane, acetylene, methylacetylene, propane, diacetylene, ethylacetylene, and butane. These gases diffuse to the lower stratosphere where temperatures are low enough to allow all seven of the aforementioned species to condense. Particle formation may not occur readily, however, as the vapor species become supersaturated. We present a theoretical analysis of particle formation mechanisms at conditions relevant to Neptune's troposphere and stratosphere and show that hydrocarbon nucleation is very inefficient under Neptunian conditions: saturation ratios much greater than unity are required for aerosol formation by either heterogeneous, ion-induced, or homogeneous nucleation. Thus, stratospheric hazes may form far below their saturation levels. We compare nucleation models with detailed atmospheric photochemical models in order to place realistic constraints on the altitude levels at which we expect hydrocarbon hazes or clouds to form on Neptune.
\r\n", "doi": "10.7907/S8F2-V423", "publication_date": "1991", "thesis_type": "phd", "thesis_year": "1991" }, { "id": "thesis:8781", "collection": "thesis", "collection_id": "8781", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03182015-092735941", "primary_object_url": { "basename": "Anderson_ww_1990.pdf", "content": "final", "filesize": 31311830, "license": "other", "mime_type": "application/pdf", "url": "/8781/1/Anderson_ww_1990.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "High Pressure States in Condensed Matter: I. High Pressure Behavior of the Iron-Sulfur System with Applications to the Earth's Core. II. Empirical Equation of State for Organic Compounds at High Pressures", "author": [ { "family_name": "Anderson", "given_name": "William Wyatt", "clpid": "Anderson-William-Wyatt" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" } ], "thesis_committee": [ { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" }, { "family_name": "Burnett", "given_name": "Donald S.", "clpid": "Burnett-D-S" }, { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Part I:
\r\n\r\nThe earth's core is generally accepted to be composed primarily of iron, with an admixture of other elements. Because the outer core is observed not to transmit shear waves at seismic frequencies, it is known to be liquid or primarily liquid. A new equation of state is presented for liquid iron, in the form of parameters for the 4th order Birch-Murnaghan and Mie-Gr\u00fcneisen equations of state. The parameters were constrained by a set of values for numerous properties compiled from the literature. A detailed theoretical model is used to constrain the P-T behavior of the heat capacity, based on recent advances in the understanding of the interatomic potentials for transition metals. At the reference pressure of 105 Pa and temperature of 1811 K (the normal melting point of Fe), the parameters are: \u03c1 = 7037 kg/m3, KS0 = 110 GPa, KS' = 4.53, KS\" = -.0337 GPa-1, and \u03b3 = 2.8, with \u03b3 \u221d \u03c1-1.17. Comparison of the properties predicted by this model with the earth model PREM indicates that the outer core is 8 to 10 % less dense than pure liquid Fe at the same conditions. The inner core is also found to be 3 to 5% less dense than pure liquid Fe, supporting the idea of a partially molten inner core. The density deficit of the outer core implies that the elements dissolved in the liquid Fe are predominantly of lower atomic weight than Fe. Of the candidate light elements favored by researchers, only sulfur readily dissolves into Fe at low pressure, which means that this element was almost certainly concentrated in the core at early times. New melting data are presented for FeS and FeS2 which indicate that the FeS2 is the S-hearing liquidus solid phase at inner core pressures. Consideration of the requirement that the inner core boundary be observable by seismological means and the freezing behavior of solutions leads to the possibility that the outer core may contain a significant fraction of solid material. It is found that convection in the outer core is not hindered if the solid particles are entrained in the fluid flow. This model for a core of Fe and S admits temperatures in the range 3450K to 4200K at the top of the core. An all liquid Fe-S outer core would require a temperature of about 4900 K at the top of the core.
\r\n\r\nPart II.
\r\n\r\nThe abundance of uses for organic compounds in the modern world results in many applications in which these materials are subjected to high pressures. This leads to the desire to be able to describe the behavior of these materials under such conditions. Unfortunately, the number of compounds is much greater than the number of experimental data available for many of the important properties. In the past, one approach that has worked well is the calculation of appropriate properties by summing the contributions from the organic functional groups making up molecules of the compounds in question. A new set of group contributions for the molar volume, volume thermal expansivity, heat capacity, and the Rao function is presented for functional groups containing C, H, and O. This set is, in most cases, limited in application to low molecular liquids. A new technique for the calculation of the pressure derivative of the bulk modulus is also presented. Comparison with data indicates that the presented technique works very well for most low molecular hydrocarbon liquids and somewhat less well for oxygen-bearing compounds. A similar comparison of previous results for polymers indicates that the existing tabulations of group contributions for this class of materials is in need of revision. There is also evidence that the Rao function contributions for polymers and low molecular compounds are somewhat different.
", "doi": "10.7907/7dsx-ed25", "publication_date": "1990", "thesis_type": "phd", "thesis_year": "1990" }, { "id": "thesis:8653", "collection": "thesis", "collection_id": "8653", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09042014-150651827", "primary_object_url": { "basename": "Blum_jd_1990.pdf", "content": "final", "filesize": 39778705, "license": "other", "mime_type": "application/pdf", "url": "/8653/1/Blum_jd_1990.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Geochemistry and Resonance Ionization of Platinum-Group Elements", "author": [ { "family_name": "Blum", "given_name": "Joel David", "clpid": "Blum-Joel-David" } ], "thesis_advisor": [ { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" }, { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" } ], "thesis_committee": [ { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" }, { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Burnett", "given_name": "Donald S.", "clpid": "Burnett-D-S" }, { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Experimental studies were conducted with the goals of 1) determining the origin of Pt-group element (PGE) alloys and associated mineral assemblages in refractory inclusions from meteorites and 2) developing a new ultrasensitive method for the in situ chemical and isotopic analysis of PGE. A general review of the geochemistry and cosmochemistry of the PGE is given, and specific research contributions are presented within the context of this broad framework.
\r\n\r\nAn important step toward understanding the cosmochemistry of the PGE is the determination of the origin of POE-rich metallic phases (most commonly \u03b5Ru-Fe) that are found in Ca, AJ-rich refractory inclusions (CAI) in C3V meteorites. These metals occur along with \u03b3Ni-Fe metals, Ni-Fe sulfides and Fe oxides in multiphase opaque assemblages. Laboratory experiments were used to show that the mineral assemblages and textures observed in opaque assemblages could be produced by sulfidation and oxidation of once homogeneous Ni-Fe-PGE metals. Phase equilibria, partitioning and diffusion kinetics were studied in the Ni-Fe-Ru system in order to quantify the conditions of opaque assemblage formation. Phase boundaries and tie lines in the Ni-Fe-Ru system were determined at 1273, 1073 and 873K using an experimental technique that allowed the investigation of a large portion of the Ni-Fe-Ru system with a single experiment at each temperature by establishing a concentration gradient within which local equilibrium between coexisting phases was maintained. A wide miscibility gap was found to be present at each temperature, separating a hexagonal close-packed \u03b5Ru-Fe phase from a face-centered cubic \u03b3Ni-Fe phase. Phase equilibria determined here for the Ni-Fe-Ru system, and phase equilibria from the literature for the Ni-Fe-S and Ni-Fe-O systems, were compared with analyses of minerals from opaque assemblages to estimate the temperature and chemical conditions of opaque assemblage formation. It was determined that opaque assemblages equilibrated at a temperature of ~770K, a sulfur fugacity 10 times higher than an equilibrium solar gas, and an oxygen fugacity 10\u2076 times higher than an equilibrium solar gas.
\r\n\r\nDiffusion rates between -\u03b3Ni-Fe and \u03b5Ru-Fe metal play a critical role in determining the time (with respect to CAI petrogenesis) and duration of the opaque assemblage equilibration process. The diffusion coefficient for Ru in Ni (DRuNi) was determined as an analog for the Ni-Fe-Ru system by the thin-film diffusion method in the temperature range of 1073 to 1673K and is given by the expression:
\r\n\r\nDRuNi (cm\u00b2 sec\u207b\u00b9) = 5.0(\u00b10.7) x 10\u207b\u00b3 exp(-2.3(\u00b10.1) x 10\u00b9\u00b2 erg mole\u207b\u00b9/RT) where R is the gas constant and T is the temperature in K. Based on the rates of dissolution and exsolution of metallic phases in the Ni-Fe-Ru system it is suggested that opaque assemblages equilibrated after the melting and crystallization of host CAI during a metamorphic event of \u2265 10\u00b3 years duration. It is inferred that opaque assemblages originated as immiscible metallic liquid droplets in the CAI silicate liquid. The bulk compositions of PGE in these precursor alloys reflects an early stage of condensation from the solar nebula and the partitioning of V between the precursor alloys and CAI silicate liquid reflects the reducing nebular conditions under which CAI were melted. The individual mineral phases now observed in opaque assemblages do not preserve an independent history prior to CAI melting and crystallization, but instead provide important information on the post-accretionary history of C3V meteorites and allow the quantification of the temperature, sulfur fugacity and oxygen fugacity of cooling planetary environments. This contrasts with previous models that called upon the formation of opaque assemblages by aggregation of phases that formed independently under highly variable conditions in the solar nebula prior to the crystallization of CAI.
\r\n\r\nAnalytical studies were carried out on PGE-rich phases from meteorites and the products of synthetic experiments using traditional electron microprobe x-ray analytical techniques. The concentrations of PGE in common minerals from meteorites and terrestrial rocks are far below the ~100 ppm detection limit of the electron microprobe. This has limited the scope of analytical studies to the very few cases where PGE are unusually enriched. To study the distribution of PGE in common minerals will require an in situ analytical technique with much lower detection limits than any methods currently in use. To overcome this limitation, resonance ionization of sputtered atoms was investigated for use as an ultrasensitive in situ analytical technique for the analysis of PGE. The mass spectrometric analysis of Os and Re was investigated using a pulsed primary Ar\u207a ion beam to provide sputtered atoms for resonance ionization mass spectrometry. An ionization scheme for Os that utilizes three resonant energy levels (including an autoionizing energy level) was investigated and found to have superior sensitivity and selectivity compared to nonresonant and one and two energy level resonant ionization schemes. An elemental selectivity for Os over Re of \u2265 10\u00b3 was demonstrated. It was found that detuning the ionizing laser from the autoionizing energy level to an arbitrary region in the ionization continuum resulted in a five-fold decrease in signal intensity and a ten-fold decrease in elemental selectivity. Osmium concentrations in synthetic metals and iron meteorites were measured to demonstrate the analytical capabilities of the technique. A linear correlation between Os\u207a signal intensity and the known Os concentration was observed over a range of nearly 10\u2074 in Os concentration with an accuracy of ~ \u00b110%, a millimum detection limit of 7 parts per billion atomic, and a useful yield of 1%. Resonance ionization of sputtered atoms samples the dominant neutral-fraction of sputtered atoms and utilizes multiphoton resonance ionization to achieve high sensitivity and to eliminate atomic and molecular interferences. Matrix effects should be small compared to secondary ion mass spectrometry because ionization occurs in the gas phase and is largely independent of the physical properties of the matrix material. Resonance ionization of sputtered atoms can be applied to in situ chemical analysis of most high ionization potential elements (including all of the PGE) in a wide range of natural and synthetic materials. The high useful yield and elemental selectivity of this method should eventually allow the in situ measurement of Os isotope ratios in some natural samples and in sample extracts enriched in PGE by fire assay fusion.
\r\n\r\nPhase equilibria and diffusion experiments have provided the basis for a reinterpretation of the origin of opaque assemblages in CAI and have yielded quantitative information on conditions in the primitive solar nebula and cooling planetary environments. Development of the method of resonance ionization of sputtered atoms for the analysis of Os has shown that this technique has wide applications in geochemistry and will for the first time allow in situ studies of the distribution of PGE at the low concentration levels at which they occur in common minerals.
", "doi": "10.7907/KXRF-AQ49", "publication_date": "1990", "thesis_type": "phd", "thesis_year": "1990" }, { "id": "thesis:7994", "collection": "thesis", "collection_id": "7994", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10172013-085025235", "primary_object_url": { "basename": "Polanskey_ca_1989.pdf", "content": "final", "filesize": 19873642, "license": "other", "mime_type": "application/pdf", "url": "/7994/1/Polanskey_ca_1989.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "I. Impact Spallation Experiments: Fracture Patterns and Spall Velocities. II. Craters in Carbonate Rocks: An Electron Paramagnetic Resonance Analysis of Shock Damage", "author": [ { "family_name": "Polanskey", "given_name": "Carol Ann", "clpid": "Polanskey-Carol-Ann" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" } ], "thesis_committee": [ { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Westphal", "given_name": "James A.", "clpid": "Westphal-J-A" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This work is divided into two independent papers.
\r\n\r\nPAPER 1.
\r\n\r\nSpall velocities were measured for nine experimental impacts into San Marcos gabbro targets. Impact velocities ranged from 1 to 6.5 km/sec. Projectiles were iron, aluminum, lead, and basalt of varying sizes. The projectile masses ranged from a 4 g lead bullet to a 0.04 g aluminum sphere. The velocities of fragments were measured from high-speed films taken of the events. The maximum spall velocity observed was 30 m/sec, or 0.56 percent of the 5.4 km/sec impact velocity. The measured velocities were compared to the spall velocities predicted by the spallation model of Melosh (1984). The compatibility between the spallation model for large planetary impacts and the results of these small scale experiments are considered in detail.
\r\n\r\nThe targets were also bisected to observe the pattern of internal fractures. A series of fractures were observed, whose location coincided with the boundary between rock subjected to the peak shock compression and a theoretical \"near surface zone\" predicted by the spallation model. Thus, between this boundary and the free surface, the target material should receive reduced levels of compressive stress as compared to the more highly shocked region below.
\r\n\r\nPAPER 2.
\r\n\r\nCarbonate samples from the nuclear explosion crater, OAK, and a terrestrial impact crater, Meteor Crater, were analyzed for shock damage using electron paramagnetic resonance, EPR. The first series of samples for OAK Crater were obtained from six boreholes within the crater, and the second series were ejecta samples recovered from the crater floor. The degree of shock damage in the carbonate material was assessed by comparing the sample spectra to spectra of Solenhofen limestone, which had been shocked to known pressures.
\r\n\r\nThe results of the OAK borehole analysis have identified a thin zone of highly shocked carbonate material underneath the crater floor. This zone has a maximum depth of approximately 200 ft below sea floor at the ground zero borehole and decreases in depth towards the crater rim. A layer of highly shocked material is also found on the surface in the vicinity of the reference bolehole, located outside the crater. This material could represent a fallout layer. The ejecta samples have experienced a range of shock pressures.
\r\n\r\nIt was also demonstrated that the EPR technique is feasible for the study of terrestrial impact craters formed in carbonate bedrock. The results for the Meteor Crater analysis suggest a slight degree of shock damage present in the \u03b2 member of the Kaibab Formation exposed in the crater walls.
", "doi": "10.7907/3rgr-f070", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:5721", "collection": "thesis", "collection_id": "5721", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04192010-095015524", "type": "thesis", "title": "Optical Radiation from Shock-Compressed Materials", "author": [ { "family_name": "Svendsen", "given_name": "Robert Frederik, Jr.", "clpid": "Svendsen-Robert-Frederik-Jr" } ], "thesis_advisor": [ { "family_name": "Kanamori", "given_name": "Hiroo", "clpid": "Kanamori-H" } ], "thesis_committee": [ { "family_name": "Kanamori", "given_name": "Hiroo", "clpid": "Kanamori-H" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Corngold", "given_name": "Noel Robert", "clpid": "Corngold-N-R" }, { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" }, { "family_name": "Harkrider", "given_name": "David G.", "clpid": "Harkrider-D-G" }, { "family_name": "Stevenson", "given_name": "David John", "clpid": "Stevenson-D-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Recent observations of shock-induced radiation from oxides, silicates and metals of geophysical interest constrain the shock-compressed temperature of these materials. In these experiments, a projectile impacts a target consisting of a metal driver plate, metal film or foil layer, and transparent window. We investigate the relationships between the temperature inferred from the observed radiation and the temperature of the shock-compressed film or foil and/or window. Changes of the temperature field in each target component away from that of their respective shock-compressed states occur because of: 1) shock-impedance mismatch between target components, 2) thermal mismatch between target components, 3) surface roughness at target interfaces, and 4) conduction within and between target components. In particular, conduction may affect the temperature of the film/foil-window interface on the time scale of the experiments, and so control the intensity and history of the dominant thermal radiation sources in the target. We use this type of model to interpret the radiation emitted by a variety of shock-compressed materials and interfaces.
\r\n\r\nIn a series of experiments on films (~ 1 \u03bcm thick) and foils (~ 10-100 \u03bcm thick) of Fe in contact with Al\u2082O\u2083 and LiF windows, Fe at Fe-Al\u2082O\u2083 interfaces releases from experimental shock-compressed states between 245 and 300 GPa to interface states at pressures between 190 and 230 GPa, respectively, and temperatures between 4000 and 8000 K, respectively. These temperatures are \u2248 200-1500 K above model calculations for Fe experiencing no reshock at ideal (smooth) Fe-Al\u2082O\u2083 interfaces. We attribute this discrepancy to localized dissipation at the Fe-Al\u2082O\u2083 interface, producing higher interface temperatures than uniform compression and energy transfer. This behavior is observed for both Fe foils and films. Both 190 GPa, localized heating due to gaps or interface-surface roughness does not apparently affect the temperature of Fe-Al\u2082O\u2083 interfaces. In contrast, from the same range of shock states, Fe at Fe-LiF interfaces releases to states between 130 and 160 GPa (because it has a lower shock impedance than Al\u2082O\u2083); both the data and model imply that Fe-LiF interfaces respond ideally to shock-compression up to 140 GPa (where the data end). Both the Fe-Al\u2082O\u2083 data and the model suggest that the degree of reshock and localized heating is strongly pressure-dependent above the solid Fe-liquid Fe phase boundary. LiF appears to be a more ideal window than Al\u2082O\u2083 also because it is a poorer thermal inertia (i. e., k\u03c1cP, where k is the thermal conductivities, \u03c1 is the mass density, and cP is the specific heat at constant pressure) match to Fe than is Al\u2082O\u2083.
\r\n\r\nIn the absence of energy sources and significant energy flux from other parts of the target, the rate of change of the film/window or foil/window, interface temperature, dTINT(t)/dt, is proportional to -\u03bcexp(-\u03bc\u00b2), where \u03bc \u2261 \u03b4FW/2\u221a(\u03baFt), \u03b4FW is the thickness of the high-temperature (reshocked) zone in the film/foil layer at the film/foil-window interface, \u03baF, is the thermal diffusivity of the film/foil material, and 0 \u2264 t \u2264 texp (texp is the time scale of the experiment, 200- 400 ns). On this basis, the temperature of a thin (\u03b4FW << 2\u221a(\u03baFtexp) reshocked layer relaxes much faster than that of a thick (\u03b4FW >> 2\u221a(\u03baFtexp)) layer. We estimate \u221a(\u03baFtexp) ~ 10 \u03bcm for Fe under the conditions of Fe-Al\u2082O\u2083 and Fe-LiF interfaces at high pressure. In this case, a 100-\u03bcm-thick reshocked Fe layer would relax very little, remaining near TINT(0) on the time scale of the experiment, while a 1-\u03bcm-thick reshocked Fe layer would relax on a time scale of \u227e 10 nsec, which is much less than texp, to a temperature just above TINT(\u221e), i.e., the temperature of the ideal (smooth) interface.
\r\n\r\nGreybody model fits to radiation from an Fe film-Al\u2082O\u2083 interface resolve a gradually increasing effective greybody emissivity, \u03b5̂gb(t), and a gradually decreasing greybody temperature, Tgb(t). This behavior is characteristic of most Fe-Al\u2082O\u2083 interface experiments. The decrease of Tgb(t) can be explained in terms of the reshock model for the film/foil-window interface temperature, TINT(t). For this experiment, the model implies that the thickness of the reshocked film layer, \u03b4FW, is approximately equal to the conduction length scale in the film, \u221a(\u03baFtexp) (~10 \u03bcm for Fe). Further, assuming 1) Tgb(t) = TINT(t), 2) the thermal inertia of the film is an order of magnitude less than the window, and \u03b4FW \u227e 2\u221a(\u03baFtexp), the greybody constrains the temperature rise due to localized heating through reshock \u0394TFW to \u227e 2000K. A slight decrease of the Al\u2082O\u2083 absorption coefficient upon shock compression can explain the slight increase of \u03b5̂gb(t) with time; this may be consistent with the low-pressure observation that the refractive index of Al\u2082O\u2083 seems to decrease with pressure.
\r\n\r\nIn contrast to the Fe-Al\u2082O\u2083 results, greybody fits to radiation from an Fe foil-LiF interface show a relatively constant greybody temperature, and a decreasing greybody emissivity. The constant greybody temperature implies a constant interface temperature, as expected for an interface experiencing minimal reshock, while the decaying \u03b5̂gb(t) is consistent with a shock-induced increase in the absorption coefficient of LiF. Setting TINT(0) = Tgb(0), we fit a simplified version of the full radiation model to these data and obtain an estimate of the absorption coefficient (~100 m\u207b\u00b9) of LIF shock-compressed to 122 GPa.
\r\n\r\nShock-compressed MgO radiates thermally at temperatures between 2900 and 3700 K in the 170-200 GPa pressure range. A simple energy-transport model of the shocked-MgO-targets allows us to distinguish between different shock-induced radiation sources in these targets and to estimate spectral absorption-coefficients, a\u03bbMgO, for shocked MgO (e.g., at 203 GPa, a\u03bbMgO ~ 6300, 7500, 4200 and 3800 m\u207b\u00b9, at 450, 600, 750 and 900 nm, respectively). The experimentally inferred temperatures of the shock-compressed states of MgO are consistent with temperatures calculated for MgO, assuming that 1) it deforms as an elastic fluid, 2) it has a Dulong-Petit value for specific heat at constant volume in its shocked-state, 3) it undergoes no phase transformation below 200 GPa, and 4) the product of the equilibrium thermodynamic Gruneisen's parameter, \u03b3, and the mass density, \u03c1, is a constant and equal to 4729.6 kg/m\u00b3.
\r\n\r\nOptical radiation from shock-compressed crystal CaMgSi\u2082O\u2086 (diopside) constrains crystal CaMgSi\u2082O\u2086 Hugoniot temperatures of 3500-4800 K in the 150-170 GPa pressure range, while glass CaMgSi\u2082O\u2086, with a density 87% of that of crystal CaMgSi\u2082O\u2086, achieves Hugoniot temperatures of 3600-3800 K in the 105-107 GPa pressure range. The radiation history of each of these materials implies that the shock-compressed states of each are highly absorptive, with effective absorption coefficients of \u2273 500-1000 m\u207b\u00b9. Calculated Hugoniot states for these materials, when compared to the experimental results, imply that crystal CaMgSi\u2082O\u2086 Hugoniot states in the 150-170 GPa range represent a high-pressure phase (HPP) solid (or possibly liquid) phase with an STP density of \u2248 4100 \u00b1 200 kg/m\u00b3, STP Gr\u00fcneisen's parameter of \u2248 1.5 \u00b1 0.5 and STP HPP-LPP specific internal energy difference, \u0394ei\u03b2-\u03b1, of 0.9 \u00b1 0.5 MJ/kg. These results are consistent with a CaSiO\u2083-MgSiO\u2083 perovskite high-pressure phase assemblage. For glass CaMgSi\u2082O\u2086, we have the same range of HPP properties, except that \u0394ei\u03b2-\u03b1, is 2.3 \u00b1 0.5 MJ/kg, a strong indication that the glass CaMgSi\u2082O\u2086 Hugoniot states occupy the liquid phase in the system CaMgSi\u2082O\u2083. Comparison of the pressure-temperature Hugoniot of crystal CaMgSi\u2082O\u2086 with the Hugoniots of its constituent oxides (i.e., SiO\u2082, CaO and MgO) demonstrates the primary influence of the HPP STP density of these materials on the magnitude of the temperature in their shock-compressed states. The crystal Di pressure-temperature Hugoniot constrained by the experimental results lies at 2500-3000 K between 110 and 135 GPa, within the plausible range of temperature profiles in the mantle near the core-mantle boundary.
\r\n\r\nIn the context of the above model considerations, we constrain the Hugoniot temperature of Fe shock-compressed to 300 GPa via thermal radiation from the Fe film/foil-window interfaces discussed above. The temperature of the film/foil-window interface is obtained from measurements of the spectral radiance of the interface, for the duration of the shock transit through the window, using a 4-wavelength optical radiometer. The model indicates that the experimental observations constrain the interface temperature, rather than the the temperature of the Al\u2082O\u2083 or LiF windows. Our results further imply that Al\u2082O\u2083 remains at least partially transparent to at least 230 GPa and ~ 9,000 K. Without correcting the Hugoniot temperatures inferred from the interface temperatures for the effects of reshock, we infer a melting temperature of Fe along its Hugoniot of 6700 \u00b1 400 K at 243 GPa. Combining these estimates with the lower-pressure (\u2264 100 GPa) static Fe melting data of Williams and Jeanloz (1986), we infer a melting temperature for Fe of approximately 7800 \u00b1 500 K at the pressure of the Earth's outer-inner boundary. Assuming that Fe or an Fe-light element alloy is forming the inner core from an Fe-light element mixture in the liquid outer core, this temperature also represents an upper bound to the temperature at the outer-inner core boundary.
\r\n\r\nLiquid-state and solid-state model fits to melting data for Fe, FeS and FeO provide constraints for calculating ideal phase relations in Fe-FeS and Fe-FeO systems in the pressure range corresponding to the earth's outer core. The liquid-state model fit to the Fe melting data of Williams and Jeanloz (1986) places constraints on the temperature and other properties along the liquidus above the range of their data. The temperature along the best-fit Fe liquidus is 5000 K at 136 GPa and 7250 K at 330 GPa, which is somewhat lower than that implied by the Hugoniot results (~ 7800 K). This discrepancy may be due to the reshock effect discussed above, or some inaccuracy in the extrapolation, presuming the Hugoniot results represent the equilibrium melting behavior of Fe. Constraints on the solidi of FeS and FeO from the comparison of data and solid-state model calculations imply that FeS and FeO melt at approximately 4610 K and 5900 K, respectively, at 136 GPa, and approximately 6150 K and 8950 K, respectively, at 330 GPa. Calculations for the equilibrium thermodynamic properties of solid and liquid Fe along the coincident solidus and liquidus imply that the entropy of melting for Fe is approximately independent of pressure at a value of approximately R (where R is Ryberg's constant), while the change in the molar heat capacity across the transition increases with pressure from approximately 0.5 R to 4R between standard pressure and 330 GPa. We use these constraints to construct ideal-mixing phase diagrams for Fe-FeS and Fe-FeO systems at outer core pressures, assuming that Fe and FeS, or Fe and FeO, respectively, are the solid phases in equilibrium with the liquid Fe-FeS or Fe-FeO mixtures, respectively.
\r\n\r\nThe composition of the Fe-X (X = 0 or S) liquid mixture relative to the eutectic composition of the Fe-FeX system determines whether Fe or FeX will solidfy at the liquidus. For these ideal mixing calculations, the eutectic composition is controlled by the ratio of the end-member (i.e., Fe and FeX) melting temperatures at a given pressure. If Fe and FeX have the same melting temperature, for example, the eutectic composition is 25 mole % X; if the melting temperature of FeX is greater or less than Fe, the eutectic composition will be displaced to more Fe or FeX rich compositions, respectively. Since, as quoted above, the melting temperature of FeO is about 1500 K greater than that of Fe at 330 GPa, which is in turn about 1000 K greater than that of FeS at this pressure, we note that calculated Fe-FeO eutectic compositions at 330 GPa (15-20 mole % O) are less than 25 mole % O, while calculated Fe-FeS eutectic compositions at 330 GPa (23-30 mole % S) are generally greater than 25 mole % S. The mass density of the Earth's outer core just above the inner core boundary is approximately 12160 kg/m\u00b3, and we note that this is also the density of an ideal mixture of 93 mole % Fe and 7 mole % S (i.e., 14 mole % FeS), and a similar mixture of approximately 72 mole % Fe and 28 mole % 0 (56 mole % FeO). Consequently, these calculations and considerations imply that an O-rich outer core is more likely to lie on the FeO-rich side of the Fe-FeX eutectic, while an S-rich outer core is more likely to lie on the Fe-rich side of the Fe-FeX eutectic.
\r\n\r\nThe temperature of the Fe-FeS eutectic is lower than the Fe-FeO eutectic, being approximately 5000 K at 330 GPa. Note that the eutectic temperature represents a lower bound to temperatures at the outer-inner core boundary under the hypothesis that this boundary represents the liquidus in an Fe-X mixture. Eutectic and end-member melting temperatures in both the Fe-FeS and Fe-FeO systems imply, in the context of the outer-inner core boundary-phase boundary hypothesis, that previous widely-accepted temperature profiles for the outer core, ranging from \u227e 3000 K at the 136 GPa, the core-mantle boundary, to \u227e 4200 K at 330 GPa, the outer-inner core boundary, are about 1000-1500 K too low. This possibility implies that at least one boundary layer of 1000-1500 K exists in the mantle, possibly at its base in the D\" region.
", "doi": "10.7907/m809-aq12", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:2928", "collection": "thesis", "collection_id": "2928", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-07192006-093757", "type": "thesis", "title": "Water Flow at the Base of a Surging Glacier", "author": [ { "family_name": "Brugman", "given_name": "Melinda Mary", "clpid": "Brugman-Melinda-Mary" } ], "thesis_advisor": [ { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-W-B" } ], "thesis_committee": [ { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-W-B" }, { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" }, { "family_name": "Epstein", "given_name": "Samuel", "clpid": "Epstein-S" }, { "family_name": "Meier", "given_name": "Mark", "clpid": "Meier-M" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Water tracing experiments were successfully conducted over a distance of ten kilometers along the base of Variegated Glacier for the purpose of characterizing the water drainage system of the glacier in the surging as compared to the non-surging state. Three tracing experiments were conducted, and fluorescent dyes, Rhodamine WT and Tinopal AMS, were injected into boreholes at separate locations. The two Rhodamine WT experiments were conducted over a 10 km distance, both during the most rapid surging motion of the glacier, and after its cessation.
\r\n\r\nIn each experiment, the terminus streams were monitored for stream discharge, sediment content and tracer concentration. Rhodamine WT tracer was significantly adsorbed on the suspended sediment, particularly during the surge. The adsorption behavior followed the Langmuir model, and calculated distribution coefficients of Kd = 100 to 1000 ml/g were measured for during the glacier surge. The Kd values measured after the surge were lower than during the surge by a factor of 10 to 1000. The much higher Kd values in the surging as compared to non-surging glacier states can be best explained by a factor of 10 to 1000 decrease in the modal and/or mean grain-size of the suspended sediment. The abundance of fine-grained sediment during the surge is probably due to increased grinding of rock material at the glacier bed.
\r\n\r\nTheoretical models of tracer dispersion in a single tunnel, were compared to models of dispersion in linked-cavity systems to infer the details of water flow at the glacier bed. The broad, roughly symmetrical, dye-return curve measured during the glacier surge conforms to diffusive dispersion theory, and differs sharply from the highly asymmetrical dispersion curve measured after the surge. Results indicate the dispersion behavior, and calculated Manning roughness, of the post-surge Variegated Glacier is similar to those of glaciers that do not surge. The drainage system of the Variegated Glacier in the surging state is consistent with a model of tracer dispersion in an interconnecting network of conduits and cavities, and is strikingly different from the tunnel system indicated for the non-surging state.
\r\n", "doi": "10.7907/VSHG-G674", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:16215", "collection": "thesis", "collection_id": "16215", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10242023-225432851", "primary_object_url": { "basename": "Schmitt_DR_1987.pdf", "content": "final", "filesize": 52360957, "license": "other", "mime_type": "application/pdf", "url": "/16215/1/Schmitt_DR_1987.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "I. Applications of Double-Exposure Holography to the Measurement of In Situ Stress and the Elastic Moduli of Rock from Boreholes. II. Shock Temperature Measurements in Fused Quartz and Crystalline NaCl to 35 GPa", "author": [ { "family_name": "Schmitt", "given_name": "Douglas Ray", "clpid": "Schmitt-Douglas-Ray" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Harkrider", "given_name": "David G.", "clpid": "Harkrider-D-G" } ], "thesis_committee": [ { "family_name": "Harkrider", "given_name": "David G.", "clpid": "Harkrider-D-G" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Clayton", "given_name": "Robert W.", "orcid": "0000-0003-3323-3508", "clpid": "Clayton-R-W" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" }, { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Part I.
\r\n\r\nThe application of a new borehole technique using holographic inter\u00ad ferometry to measure the in situ state of stress and the modulus of elasti\u00adcity of rock is discussed. The apparatus exposes two holograms which are taken both before and after micron scale displacements are induced by\r\n(1) drilling a small stress-relieving hole in the wall of a borehole, and (2) applying a normal point force to the borehole wall. Maximum induced displacements are approximately 10 microns; the holograms are sensitive to movements on the order of 0.1 micron. Raw data take the form of a series interference holograms which have dark fringes superimposed on the three dimensional holographic borehole wall image. Synthetic fringe patterns are used to forward model the observed in the present method of data analysis. Calibrations of the normal force method of measuring the elastic moduli is carried out on metals with well defined elastic properties. Typi\u00adcally each test yields elastic (Young's) moduli for brass and aluminum of 100 \u00b1 10 GPa and 70 \u00b1 5 GPa, respectively, which are in close agreement with\r\nstandard tests. Laboratory holographic measurements of the Young's modulus on a sample of keragenaceous dolomitic marlstone (taken from the same mine as which the in situ experiments were conducted) yielded 16.8 \u00b1 2.8 GPa in agreement with the predicted modulus of 17.2 \u00b1 2.0 GPa based upon published density-modulus relationships. Sonic velocity determinations of the dynamic Young's modulus on cores taken from the rock sample give values consistent with the holographic measurements of 13.5 to 19.1 GPa for assumed values of Poisson's ratio of 0.35 to 0.25. The results of field tests in a horizontal borehole in a mine pillar in the Mahogany formation of Garfield County, Colorado, are presented for both experiments. The elastic modulus was found to vary with position in the borehole from 26.9 to 36.0 GPa. The farfield stresses for a borehole station 4 m from the mine pillar free surface were found from analysis of several stress-relief holograms; the determined vertical stress within the mine pillar was -10.2 MPa (compressive) close to the predicted magnitude of -11.2 MPa.
\r\n\r\nPart II.
\r\n\r\nGreybody temperatures and emittances of fused quartz under shock compression between 10 and 30 GPa are determined. Observed radiative temperatures are higher than computed continuum temperatures for shock compressed fused quartz, however; below ~26 GPa observed emittances are < 0.02. This suggests that fused quartz deforms heterogeneously in this shock pressure range, as has been observed in other minerals. Between 10 and 16 GPa, radiative temperatures decrease from 4400 K to 3200 K, above 16 GPa to 30 GPa greybody temperatures of ~3000 K with low emit\u00adtances are observed. The emittances increase with pressure from 0.02 to 0.9. The pressure range from 10 to 16 GPa coincides with the permanent densification region while the 16 to 30 GPa range coincides with the mixed phase region along the fused quartz Hugoniot. The differing radiative behaviors relate to these modes of deformation. Based upon shock recovery experiments and a proposed model of heterogeneous deformation under shock compression, the temperatures associated with low emittances in the mixed phase region probably represents the melting temperature of the high pressure phase. Above 20 GPa to 30 GPa the melting temperature of stishovite would therefore be approximately 3000 K and almost independent of pressure. The effect of pressure on melting relations for the phase system SiO\u2082-Mg\u2082SiO\u2084 are considered together with the proposed melting curve of stishovite and suggest that maximum solidus temperatures within the mantle of ~2370 K at 12.5 GPa and ~2520 K at 20.0 GPa. Using the proposed stishovite melting temperatures (T_m) and reasonable upper mantle temperatures (T), the effective viscosity (which is a function of the homologous temperature (T_m/T)) appears to remain nearly constant from 600 to 200 km depth in the Earth.
\r\n\r\nRadiative color temperatures were measured in single crystal sodium chloride under shock compression parallel to [100] over a pressure range from 20 to 35 GPa. Color temperatures from 2500 to 4500 K and emittances from 0.003 to 0.3 were determined by fitting observed spectra (450 to 850 nm) to the Planck greybody radiation law. These data support a heterogeneous shock deformation model of shocked halite in this pressure range. A 2500 K temperature rise is observed over the Bl-B2 mixed phase region from 25 to 30 GPa. Assuming that shock deformation occurs via yielding in localized planar zones which become melt and the melting temperature at high pressure controls the temperature, we infer that the temperature of the B2 fusion curve from 30 to 35 GPa rises from 3200 to 3300 K. The Bl-B2-liquid triple point is predicted at a temperature of 2250 K and 23.5 GPa.
", "doi": "10.7907/vr7c-6j57", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:11448", "collection": "thesis", "collection_id": "11448", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04052019-172938000", "type": "thesis", "title": "Magmons: Solitary Waves Arising in the Buoyant Ascent of Magma by Porous Flow through a Viscously Deformable Matrix", "author": [ { "family_name": "Scott", "given_name": "David Russell", "clpid": "Scott-David-Russell" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" }, { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" }, { "family_name": "Stevenson", "given_name": "David John", "clpid": "Stevenson-D-J" }, { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The dynamics of partially molten regions of the Earth's mantle are studied using a combination of theoretical, experimental, and numerical techniques. The physical model is based on experimental observations of partially molten ultramafic rocks and incorporates two elements: buoyancy-driven porous flow of magma through a viscously deformable matrix, and buoyancy-driven circulation of the whole rock.
\r\n\r\nThe first element of this model is analogous to buoyancy-driven pipe flow of a liquid through a denser and more viscous wall fluid. Laboratory experiments on this system illustrate the phenomenon of solitary waves. These are waves of larger pipe radius that ascend a uniform pipe of smaller radius. The waves are very nearly conserved in collisions. These, and the corresponding waves of higher porosity that arise in one-dimensional porous flow, are characterized further by analysis and numerical experiments.
\r\n\r\nThe full system, incorporating circulation in a multidimensional porous medium, also displays solitary waves governed by the same basic processes as the one-dimensional waves. Analysis and numerical experiments show that the multidimensional waves have a circular or spherical form.
\r\n\r\nA possible natural manifestation of this fluid dynamical phenomenon is in igneous processes. Magmons, as the waves are called in that setting, probably have wavelengths of kilometers and velocities of centimeters per year. Magma ascent in magmons may account for episodicity in igneous emplacement. Also, a magmon can collect and mobilize a small degree of partial melt without disturbing its geochemical signature. In a partially molten region the characteristic wavelength of magmons will always be superimposed on that of large scale variations in porosity.
", "doi": "10.7907/mvdj-ty73", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:6712", "collection": "thesis", "collection_id": "6712", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10132011-090721112", "primary_object_url": { "basename": "Vidale_je_1987.pdf", "content": "final", "filesize": 24558213, "license": "other", "mime_type": "application/pdf", "url": "/6712/1/Vidale_je_1987.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Application of Two-Dimensional Finite-Difference Wave Simulation to Earthquakes, Earth Structure, and Seismic Hazard", "author": [ { "family_name": "Vidale", "given_name": "John Emilio", "clpid": "Vidale-John-Emilio" } ], "thesis_advisor": [ { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" }, { "family_name": "Clayton", "given_name": "Robert W.", "orcid": "0000-0003-3323-3508", "clpid": "Clayton-R-W" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" }, { "family_name": "Clayton", "given_name": "Robert W.", "orcid": "0000-0003-3323-3508", "clpid": "Clayton-R-W" }, { "family_name": "Jennings", "given_name": "Paul C.", "clpid": "Jennings-P-C" }, { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Although the earth is 3-dimensional (3-D), numerical simulations of wave propagation through laterally heterogeneous media are easier to formulate and more practical to use in 2-D. In this thesis, schemes to model seismic wave propagation through laterally varying structures with 2-D numerical algorithms are developed and applied to earthquake and explosion problems.
\r\n\r\nIn Chapter 1, 2-D source expressions that have the same radiation patterns as their 3-D counterparts are derived which can rectify the following three problems: the use of 2-D simulations generally results in \"line source tails\" on what would be impulsive arrivals in 3-D, 1/\u221aR rather than 1/R amplitude decay for body waves, and no decay rather than 1/\u221aR amplitude decay for surface waves. Because this technique approximately transforms waves from a cartesian 2-D grid to a cylindrically symmetric 3-D world, slightly anisotropic geometrical spreading in 2-D better approximates isotropic spreading in 3-D than simple isotropic spreading in 2-D does. In Section 1.7, a correction to the explosive source expression reduces energy traveling vertically out of the source region, but leaves unchanged the energy traveling laterally out of the source region. In some cases, this correction will significantly improve the results of using a 2-D grid to simulate elastic wave propagation from an explosive point source.
\r\n\r\nIn Chapter 2, synthetic seismograms are constructed for the strong motions of the 1968 Borrego Mountain earthquake recorded at EI Centro. A good fit to the data results from using the laterally varying model determined by a detailed refraction survey and the source parameters determined by teleseismic waveform modeling. Shallow faulting is no longer necessary to explain the long-period surface-wave development.
\r\n\r\nSynthetic seismograms calculated for the 1971 San Fernando earthquake show strong effects due to lateral variation in sediment thickness in the San Fernando valley and the Los Angeles basin. Using previously determined basin structure and teleseismically determined source parameters, two-dimensional SH and P-SV finite difference calculations can reproduce the amplitude and duration of the strong motion velocities recorded across the basins in Los Angeles in the period range from 1 to 10 seconds. The edges of basins nearest the seismic source show ground motion amplification up to a factor of three, and tend to convert direct shear waves into Love and Rayleigh waves that travel within the basins. The computed motions are sensitive to the mechanism and location of earthquakes. A strike-slip earthquake on the Newport-Inglewood fault zone, for example, would produce different patterns of peak velocity and duration of shaking across the San Fernando and Los Angeles basins.
\r\n\r\nIn Chapter 3, the effect of shallow station structure and lateral velocity variation are investigated for records of the Amchitka explosion Milrow. The differences between the Meuller-Murphy, Heimberger-Hadley, and von Seggern-Blandford reduced displacement potential (RDP) source representations are small compared to the differences between using various possible velocity structures.
\r\n\r\nCreager and Jordan (1986) propose that penetration of subducting slabs under the Kurile Islands and other subduction zones to depths of at least 1000 km is necessary to explain the t ravel time anomalies of deep earthquakes. Such penetration would also affect the amplitudes and waveforms of the body waves from these earthquakes. In Chapter 4, synthetic seismograms appropriate for a record section in a plane perpendicular to the strike of the slab are presented using a coupled finite-difference and Kirchhoff method. An inferred shear-wave version of the compressional-wave velocity structure of Creager and Jordan (1986) produces an amplitude decrease up to a factor of four and waveform broadening up to 20 seconds for SH arrivals with a take-off angle pointing straight down t he slab. Slabs that extend only 300 km below the earthquake but are half as thick and twice as anomalously fast as Creager and Jordan 's (1986) velocity model will roughly preserve the travel time variation pattern, and show less waveform broadening, but produce first arrivals that are emergent. Slabs that become thicker with depth show less waveform broadening. Reconciliation of the amplitude, waveform distort ion, and timing of body waves from deep events is necessary to understand the geometry of slabs near and below the 6.50 km discontinuity.
", "doi": "10.7907/7TQ9-X746", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:9559", "collection": "thesis", "collection_id": "9559", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02122016-151411807", "type": "thesis", "title": "Dynamical Models for the Earth's Geoid", "author": [ { "family_name": "Richards", "given_name": "Mark Alan", "orcid": "0000-0002-1893-953X", "clpid": "Richards-Mark-Alan" } ], "thesis_advisor": [ { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" }, { "family_name": "Clayton", "given_name": "Robert W.", "orcid": "0000-0003-3323-3508", "clpid": "Clayton-R-W" }, { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" }, { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The Earth's largest geoid anomalies occur at the lowest spherical harmonic degrees, or longest wavelengths, and are primarily the result of mantle convection. Thermal density contrasts due to convection are partially compensated by boundary deformations due to viscous flow whose effects must be included in order to obtain a dynamically consistent model for the geoid. These deformations occur rapidly with respect to the timescale for convection, and we have analytically calculated geoid response kernels for steady-state, viscous, incompressible, self-gravitating, layered Earth models which include the deformation of boundaries due to internal loads. Both the sign and magnitude of geoid anomalies depend strongly upon the viscosity structure of the mantle as well as the possible presence of chemical layering.
\r\n\r\nCorrelations of various global geophysical data sets with the observed geoid can be used to construct theoretical geoid models which constrain the dynamics of mantle convection. Surface features such as topography and plate velocities are not obviously related to the low-degree geoid, with the exception of subduction zones which are characterized by geoid highs (degrees 4-9). Recent models for seismic heterogeneity in the mantle provide additional constraints, and much of the low-degree (2-3) geoid can be attributed to seismically inferred density anomalies in the lower mantle. The Earth's largest geoid highs are underlain by low density material in the lower mantle, thus requiring compensating deformations of the Earth's surface. A dynamical model for whole mantle convection with a low viscosity upper mantle can explain these observations and successfully predicts more than 80% of the observed geoid variance.
\r\n\r\nTemperature variations associated with density anomalies in the man tie cause lateral viscosity variations whose effects are not included in the analytical models. However, perturbation theory and numerical tests show that broad-scale lateral viscosity variations are much less important than radial variations; in this respect, geoid models, which depend upon steady-state surface deformations, may provide more reliable constraints on mantle structure than inferences from transient phenomena such as postglacial rebound. Stronger, smaller-scale viscosity variations associated with mantle plumes and subducting slabs may be more important. On the basis of numerical modelling of low viscosity plumes, we conclude that the global association of geoid highs (after slab effects are removed) with hotspots and, perhaps, mantle plumes, is the result of hot, upwelling material in the lower mantle; this conclusion does not depend strongly upon plume rheology. The global distribution of hotspots and the dominant, low-degree geoid highs may correspond to a dominant mode of convection stabilized by the ancient Pangean continental assemblage.
", "doi": "10.7907/ncf0-0c06", "publication_date": "1986", "thesis_type": "phd", "thesis_year": "1986" }, { "id": "thesis:11789", "collection": "thesis", "collection_id": "11789", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09032019-144830666", "primary_object_url": { "basename": "Fine_GJ_1986.pdf", "content": "final", "filesize": 42465709, "license": "other", "mime_type": "application/pdf", "url": "/11789/1/Fine_GJ_1986.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Carbon Dioxide in Synthetic and Natural Silicate Glasses", "author": [ { "family_name": "Fine", "given_name": "Gerald Jonathan", "clpid": "Fine-Gerald-Jonathan" } ], "thesis_advisor": [ { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" } ], "thesis_committee": [ { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" }, { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" }, { "family_name": "Wyllie", "given_name": "Peter J.", "clpid": "Wyllie-P-J" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" }, { "family_name": "Epstein", "given_name": "Samuel", "clpid": "Epstein-S" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Infrared spectroscopy has been used to study the speciation of CO2 in both synthetic silicate glasses quenched from melts held at high temperatures and pressures and in natural basaltic glasses. In glasses near the NaAlO2-SiO2 join, absorption bands resulting from the antisymmetric stretches of both molecular CO2 (2352 cm-1) and CO2-3 (1610 cm-1 and 1375 cm-1) are observed. The latter are attributed to distorted Na-carbonate ionic-complexes. Molar absorptivities for each of the absorption bands have been determined; these molar absorptivities allow the quantitative determination of species concentrations in sodium aluminosilicate glasses with a precision on the order of several percent of the amount present. The accuracy of the method is estimated to be \u00b115-20% at present.
\r\n\r\nThe ratio of molecular CO2 to CO2-3 in sodium aluminosilicate glasses varies little for each silicate composition over the range of total dissolved CO2 contents (0-1.5%), pressures (15-33 kbar) and temperatures (1400-1560\u00b0C) studied. This ratio is, however, a strong function of silicate composition, increasing both with decreasing Na2O content along the NaAlO2-SiO2 join and with decreasing Na2O content in peraluminous compositions off the join.
\r\n\r\nThe molar absorptivities determined for sodium aluminosilicate glasses have also been used to measure the concentrations of CO2 in albitic (NaAlSi3O8) glasses quenched from melts equilibrated with CO2 vapor at high pressures (15-30 kbar) and temperatures (1450-1625\u00b0C). The results show that total CO2 solubility increases with increasing pressure at constant temperature. Both molecular CO2 and CO2-3 concentrations increase with pressure. At constant pressure, the solubility of molecular CO2 decreases with temperature while the concentration of CO2-3 increases. The net effect is that total CO2 solubility is not significantly dependent on temperature, decreasing slightly with increasing temperature at constant pressure.
\r\n\r\nThe speciation of CO2 in both synthetic Ca \u00b1 Mg-composition glasses and natural basaltic glasses contrasts with the case of CO2-bearing sodium aluminosilicate glasses. CO2 is inferred to be dissolved in these glasses as distorted Ca- or Mg-carbonate ionic-complexes that result in unique infrared absorption bands at 1515 cm-1 and 1435 cm-1. The molar absorptivities for each of these absorption bands were also determined. No detectable molecular CO2 is dissolved in these glasses.
\r\n\r\nInfrared spectroscopic measurements of species concentrations in glasses provide insights into the molecular level processes accompanying CO2 solution in melts and can be used to test and constrain thermodynamic models of CO2-bearing melts. CO2 speciation in silicate melts can be modelled by equilibria between molecular CO2, CO2-3, and oxygen species in the melts. Consideration of the thermodynamics of such equilibria can account for the observed linear relationship between molecular CO2 and carbonate concentrations in sodium aluminosilicate glasses, the absence of molecular CO2 in Ca \u00b1 Mg silicate glasses, the proposed linear relationship between total dissolved CO2 content and the activity of CO2 in melts, and observed variations in CO2 solubility in melts.
\r\n\r\nDissolved CO2 contents of natural basaltic glasses can also be determined from the intensities of the carbonate absorption bands at 1515 cm-1 and 1435 cm-1. The uncertainty of the method is estimated to be \u00b115% of the amount present. The infrared technique is a powerful tool for the measurement of dissolved CO2 contents in natural basaltic glasses since it is nondestructive, can be aimed at regions of glass a few tens of micrometers in size, and discriminates between dissolved carbonate and carbon present as carbonate alteration, contained in fluid inclusions or adsorbed on the glass.
\r\n\r\nA set of submarine basaltic glasses dredged from a variety of locations contain 0-400 ppm dissolved CO2, measured using the infrared technique. These concentrations are lower than most previous reports for similar basaltic glasses. No general relationship is observed between dissolved CO2 content and depth of magmatic eruption.
", "doi": "10.7907/xmqc-xv31", "publication_date": "1986", "thesis_type": "phd", "thesis_year": "1986" }, { "id": "thesis:16216", "collection": "thesis", "collection_id": "16216", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10272023-170924439", "primary_object_url": { "basename": "Rigden_SM_1986.pdf", "content": "final", "filesize": 48886487, "license": "other", "mime_type": "application/pdf", "url": "/16216/1/Rigden_SM_1986.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "The Determination of the Equation of State of Molten Silicates at High Pressures Using Shock-Wave Techniques", "author": [ { "family_name": "Rigden", "given_name": "Sally Miranda", "clpid": "Rigden-Sally-Miranda" } ], "thesis_advisor": [ { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" } ], "thesis_committee": [ { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" }, { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" }, { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Shock wave (Hugoniot) equation-of state experiments have been carried out on molten silicates in the petrologically important system CaMgSi\u2082O\u2086-CaAl\u2082Si\u2082O\u2088 via the projectile impact method. An RF heating technique was developed to heat silicate samples contained in pure Mo containers to the necessary high initial temperatures (up to 1773 K). Thermocouple techniques, a refractory sample holding system and optical shutter systems, were developed to allow utilization of a propellant gun apparatus at impact velocities ranging from 1.0 to 2.5 km sec\u207b\u00b9 corresponding to shock pressures of 4 to 40 GPa. The methodology for taking into account the effect of the Mo container in measuring the equation of state of the molten silicate is explicitly derived.
\r\n\r\nResults on molten diopside (CaMgSi\u2082O\u2086), anorthite (CaAl\u2082Si\u2082O\u2088) and an inter\u00ad mediate composition (36 mole % CaAl\u2082Si\u2082O\u2088, 64 mole % CaMgSi\u2082O\u2086: An_(0.36)Di_(0.64)) are presented. Reduction of the Hugoniot data for these materials to third-order Birch-\u00adMurnaghan isentropes yields 1 atm bulk moduli (K_s) in the range 18-24 GPa which are in good agreement with bulk moduli recently measured by ultrasonic methods at 1 atm and similar temperatures. The pressure derivatives of bulk modulus (K') vary\r\nfrom 5-7. Shock temperature calculations for An_(0.36)Di_(0.64) indicate temperatures of 2400-2600 K at ~25 GPa. The Hugoniot states are believed to lie metastably in the liquid field on the basis of measured bulk modulus, calculated Hugoniot density of a solid of the same composition and estimated crystallization times.
\r\n\r\nThe measured equation of state data for molten diopside is used in conjunction with other thermochemical data to constrain the diopside solidus via the Clausius\u00ad Clapeyron equation at pressures up to 20 GPa. The present data are consistent with\r\n measured fusion curve data of others to 5 GPa. Above ~10 GPa, a marked shallowing of the solidus is predicted as the difference in volume between crystalline and mol\u00adten diopside in equilibrium approaches zero.
\r\n\r\nComparison of the results for molten diopside with those from the intermediate composition indicates that the liquids exhibit ideal mixing behavior with respect to volume to within \u00b12% up to ~40 Gpa. Gradual changes in coordination of Al\u00b3\u207a and Si\u2074\u207a from tetrahedral at low pressures to octahedral at high pressures are believed to occur during compression of these materials. The integrated compressibility as reflected in the values of K_s and K' is related to the proportion of tetrahedrally coordinated cations at low pressure, and the volume at ~40 GPa is from 100-110% of that of a mixture of the dense, high-pressure phases MgSiO\u2083 (perovskite), CaSiO\u2083 (perovskite), Al\u2082P\u2083 (corundum) and SiO\u2082 (stishovite).
\r\n\r\nImportant petrological implications of our results include: (1) basic to ultrabasic melts become denser than olivine- and pyroxene-rich mantle at pressures of 6-10 GPa, and (2) there is a maximum depth from which basaltic melt can rise buoyantly within terrestrial planetary interiors.
", "doi": "10.7907/5v04-ws14", "publication_date": "1986", "thesis_type": "phd", "thesis_year": "1986" }, { "id": "thesis:899", "collection": "thesis", "collection_id": "899", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03082008-083041", "primary_object_url": { "basename": "Schwendeman_dw_1986.pdf", "content": "final", "filesize": 5610554, "license": "other", "mime_type": "application/pdf", "url": "/899/1/Schwendeman_dw_1986.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Numerical Shock Propagation Using Geometrical Shock Dynamics", "author": [ { "family_name": "Schwendeman", "given_name": "Donald William", "orcid": "0000-0002-0161-5221", "clpid": "Schwendeman-Donald-William" } ], "thesis_advisor": [ { "family_name": "Whitham", "given_name": "Gerald Beresford", "clpid": "Whitham-G-B" } ], "thesis_committee": [ { "family_name": "Whitham", "given_name": "Gerald Beresford", "clpid": "Whitham-G-B" }, { "family_name": "Keller", "given_name": "Herbert Bishop", "clpid": "Keller-H-B" }, { "family_name": "Lorenz", "given_name": "Jens", "clpid": "Lorenz-Jens" }, { "family_name": "Sturtevant", "given_name": "Bradford", "clpid": "Sturtevant-B" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Various numerical schemes are developed to calculate the motion of shock waves in gases based on Whitham's theory of geometrical shock dynamics. The basic numerical scheme is used to study the propagation of two-dimensional shock waves along walls and in channels, and the self-focusing of initially curved shock- fronts. This scheme is extended to treat shock wave motion in non-uniform media. The extended scheme is used to examine shock wave refraction at both planar and curved interfaces separating gases with different properties. Precursor-irregular refraction patterns are obtained using geometrical shock dynamics. A general numerical scheme designed to propagate a shock surface in three dimensions is presented. Three-dimensional shock focusing and shock propagation in a curved pipe are considered primarily to demonstrate the use of the three-dimensional numerical scheme. The reflection of planar shock waves from curved walls is studied. The motion of the shock is determined using the combined theories of regular reflection and geometrical shock dynamics. A numerical scheme based on the combined theories is discussed. The numerical scheme is used to calculate the reflection and subsequent focusing of weak planar shock waves. Some of the present results are compared with other solutions to the equations of geometrical shock dynamics obtained using different methods. Recent experimental investigations are discussed and compared with our results calculated using geometrical shock dynamics.
\r\n", "doi": "10.7907/Q5VX-AF72", "publication_date": "1986", "thesis_type": "phd", "thesis_year": "1986" }, { "id": "thesis:1047", "collection": "thesis", "collection_id": "1047", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03212008-081007", "primary_object_url": { "basename": "Atzmon_m_1986.pdf", "content": "final", "filesize": 4573964, "license": "other", "mime_type": "application/pdf", "url": "/1047/1/Atzmon_m_1986.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "A Study of Bulk Amorphous Alloys Formed by Solid-State Reaction in Elemental Composites", "author": [ { "family_name": "Atzmon", "given_name": "Michael", "orcid": "0000-0002-7055-1313", "clpid": "Atzmon-Michael" } ], "thesis_advisor": [ { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" } ], "thesis_committee": [ { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Tombrello", "given_name": "Thomas A.", "clpid": "Tombrello-T-A" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Nicolet", "given_name": "Marc-Aurele", "clpid": "Nicolet-M-A" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Bulk amorphous Zr- and Er- based alloys have been synthesized by solid-state reaction in elemental composites prepared by mechanical deformation. For the Er- based composites, complete amorphization was achieved by near- isothermal rolling near room temperature. The driving force for the reaction was found to be a large negative enthalpy of mixing between the constituent elements. Strain and interfacial energies have been estimated and found to modify the driving force only slightly. X-ray diffraction and differential scanning calorimetry have been used to characterize the structure and crystallization behavior of the alloys obtained. Comparison to corresponding amorphous alloys prepared by liquid quenching and sputtering gave good agreement.
\r\n\r\nThe diffusion of Au in amorphous Au-Y and Au-La thin films produced by co-evaporation has been studied by means of X-ray diffraction and Rutherford backscattering. An estimated diffusion coefficient agrees with those obtained by other authors for diffusion of Au in several amorphous alloys. The results confirm that there can be bulk self-diffusion in an amorphous alloy without crystallization. Thus, one does not need to assume short-circuit diffusion during the growth of an amorphous phase by solid-state reaction.
", "doi": "10.7907/5M6N-SK53", "publication_date": "1986", "thesis_type": "phd", "thesis_year": "1986" }, { "id": "thesis:7477", "collection": "thesis", "collection_id": "7477", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02142013-085850235", "type": "thesis", "title": "Studies of the Crust-Mantle System Beneath Southern California", "author": [ { "family_name": "Humphreys", "given_name": "Eugene Drake", "orcid": "0000-0002-1916-8378", "clpid": "Humphreys-Eugene-Drake" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "thesis_committee": [ { "family_name": "Clayton", "given_name": "Robert W.", "orcid": "0000-0003-3323-3508", "clpid": "Clayton-R-W" }, { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "A back-projection method of tomographic reconstruction is adapted to inverted seismic travel-time data. The problems encountered in inverting these data include ray set inhomogeneity and anisotropy and the three-dimensionality of the space interrogated. Jacobi iteration, deconvolution and variable ray weighting are shown to work well in augmenting the basic back-projection method to produce a well-focused image. Applications of the various focusing algorithms are shown to have a degree of success that depends on the ray geometry used. Also, the ability to reconstruct an accurate image when the data include moderate amounts of noise is shown to be good.
\r\n\r\nP-wave teleseismic travel time delays recorded by the southern California array are inverted with the tomographic method to obtain variations in the P-wave velocity structure to a depth of 750 km. Two major anomalies are imaged. A curtain-like E-W trending high velocity feature is found directly beneath the Transverse Ranges. This feature is about 50 km in thickness, extends in depth to a maximum of about 250 km on its eastern end, and attains a maximum velocity that is about 3% greater than average mantle at the same depth beneath southern California. A zone of low-velocity material is found in the uppermost 100 km beneath the region of the Salton Trough. The seismic velocities here are depressed by about 4%.
\r\n\r\nThese anomalous regions are interpreted to be related to the geologic processes that have been active recently in southern California. Scaling relations are used to estimate that the Transverse Range anomaly is about 500\u00b0C colder and 1% more dense than average southern California mantle of the same depth, while the Salton Trough anomaly is about 1/2% less dense and contains about 3% melt. The density distribution drives a flow of upper mantle material from the Salton Trough region towards the Transverse Ranges, where it sinks into the mantle to form the feature seen beneath these ranges. Mantle flow results in tractions that act on the base of the lithosphere to produce stresses within the lithosphere that are tensile in the Salton Trough and compressive in the Transverse Ranges. These stresses are thought to account for the physiography seen in these provences.
\r\n\r\nThe southern California crust is modeled using late Quaternary slip rates on major faults, and a kinematic description is determined that has: 1) only local sites of convergence in the Transverse Ranges, and 2) the occurrance of significant strain rates near to the southern California coast, including the western Transverse Ranges.
", "doi": "10.7907/j2xf-gq29", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:3656", "collection": "thesis", "collection_id": "3656", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09202002-161800", "primary_object_url": { "basename": "Kasiraj_p_1985.pdf", "content": "final", "filesize": 24311743, "license": "other", "mime_type": "application/pdf", "url": "/3656/1/Kasiraj_p_1985.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Shock-Wave Consolidation of Metallic Powders", "author": [ { "family_name": "Kasiraj", "given_name": "Prakash", "clpid": "Kasiraj-Prakash" } ], "thesis_advisor": [ { "family_name": "Vreeland", "given_name": "Thad", "clpid": "Vreeland-T" } ], "thesis_committee": [ { "family_name": "Vreeland", "given_name": "Thad", "clpid": "Vreeland-T" }, { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Tombrello", "given_name": "Thomas A.", "clpid": "Tombrello-T-A" }, { "family_name": "Sturtevant", "given_name": "Bradford", "clpid": "Sturtevant-B" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Conventional powder metallurgical techniques have the drawback in that metastable properties of the powder can be lost during the sintering stage. The use of shock waves to bond particles of powder together can, in principle, circumvent this drawback and produce bulk solids which retain metastable properties of the initial powder. However, the effects of the relevant shock and powder parameters on the final properties of the compacts must be understood before this technique can be used optimally.
\r\n\r\nIn the present investigation the influence of shock pressure, shock duration, and surface oxides on the mechanical and metallurgical properties of compacted steel, molybdenum, and nickel-molybdenum alloy powders were studied. In addition, to improve our fundamental understanding of shock waves in metallic powder media, the shock temperature at the junction between two layers of copper and constantan powders was measured via the thermoelectric effect for varying shock pressure and energy.
\r\n\r\nThe measured homogeneous temperatures in the copper-constantan powders varied from 150 C to 940 C as the shock energy was increased from 50 to 360 kJ/kg (shock pressure from 1.3 to 9.4 GPa). These results indicate that almost all of the energy in the shock front is converted into thermal energy. Furthermore, the rise time of the shock front is less than 23 ns which corresponds to a shock front width of less than 37 \u00b5m,a dimension comparable to the powder particle diameter.
\r\n\t\r\nRapidly solidified AISI 9310 steel powders were consolidated and the dependence of the microhardness and the ultimate tensile strength of the compacts on the shock energy from 94 to 770 kJ/kg (3.6 to 19.0 GPa) were measured for an initial powder distension of 1.64 and a shock duration of 2-3 \u00b5s. Photomicrographs and SEM fractographs were used to study the interparticle bonding in the compacts. Results show that, for shock energies below 200 kJ/kg (4.9 GPa), the compacts have negligble strength. However, above this threshold the strength of the compact rises rapidly until a maximum value of 1.3 GPa is reached at a shock energy of 500 kJ/kg (12.4 GPa). This strength which is larger than that of wrought AISI 9310 remains constant before decreasing at the higher shock energies. In marked contrast, with increasing shock energy, the diamond pyramid hardness increases very gradually from a value of 340 for the initial powder to 500 at a shock energy of 500 kJ/kg. Microhardness also begins to decrease at higher shock energies. The maximum strength obtained correlates well with the strength expected from microhardness measurements.
\r\n\r\nThe AISI 9310 powders were also used to study the effect of shock duration on the compact's strength. Results indicate that, for consolidations with a shock energy of 400 kJ/kg (10 GPa), shock durations greater than 0.4 \u00b5s are needed to produce strong compacts. This lower limit on shock duration can be attributed to the condition that the duration of the compressive shock wave must exceed the solidification and strengthening time of the melt produced by the shock wave.
\r\n\t\r\nMolybdenum powders with a distension of 1.67 were used to study the effect of surface oxides. Results indicate that, by reducing the surface oxides, the tensile strength of the compact can be increased from nearly zero to 0.76 GPa for a shock energy of 580 kJ/kg (17.8 GPa). The final strength is comparable to that of bar stock of molybdenum.
\r\n\t\r\nPowders of glass forming Mark-1064 alloy (Ni55.8Mo25.7Cr9.7B8.8) with a distension of 2.0 were used to study the amount of melt produced during the shock consolidation process. Such measurements were possible because the melt was quenched rapidly enough to form the amorphous phase which could be delineated from the microcrystalline phase during metallographic examination. The results indicate that shock energies above 190 kJ/kg (3.4 GPa) are required before the occurence of measurable melting. The amount of melt is much less than the upper bound limit and the melt distribution is nonuniform.
\r\n\t\r\nFinally, the conceptual understanding of the shock consolidation process is discussed and the criteria for producing well-bonded compacts are enumerated. These criteria can be conveniently expressed in terms of a shock consolidation map which plots a dimensionless shock duration versus a dimensionless shock energy. The existing models for the shock consolidation process are evaluated in light of the recently acquired results.
", "doi": "10.7907/7cxy-vx62", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:1179", "collection": "thesis", "collection_id": "1179", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03272008-075843", "primary_object_url": { "basename": "Hazelton_le_1985.pdf", "content": "final", "filesize": 18242265, "license": "other", "mime_type": "application/pdf", "url": "/1179/1/Hazelton_le_1985.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "A Study of Hydrogen Mobility in a Glassy Zr\u2082Pd Using Internal Friction", "author": [ { "family_name": "Hazelton", "given_name": "Lowell Eugene", "orcid": "0000-0002-4616-6423", "clpid": "Hazelton-Lowell-Eugene" } ], "thesis_advisor": [ { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" } ], "thesis_committee": [ { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Culick", "given_name": "Fred E. C.", "clpid": "Culick-F-E-C" }, { "family_name": "Vreeland", "given_name": "Thad", "clpid": "Vreeland-T" }, { "family_name": "Nicolet", "given_name": "Marc-Aurele", "clpid": "Nicolet-M-A" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Hydrogen-related internal friction peaks have been measured in amorphous Zr2Pd and Y64Fe36, covering a range of hydrogen concentrations up to 0.86 H/M for the former alloy. The internal friction peaks were found to be several times wider than a peak due to a single relaxing defect, and quite asymmetric with a long low temperature tail, as with previous measurements on hydrogen in amorphous metals. They showed a thermally activated relaxation time with a frequency prefactor and a range of activation energies indicative of a point defect source. The evidence is shown to strongly indicate a Snoek-type defect, consisting of single hydrogen atoms in interstitial sites with strongly elliptical or variable strain dipole tensors. The integral equation that gives the internal friction is inverted for the first time to yield the distribution of relaxation times. It is suggested that the main peak in the resulting distribution of activation energies results from hydrogen hopping through three-sided faces, primarily between tetrahedral sites. These sites are found to change at high concentration to have a lower strain dipole ellipticity and to become more well-defined. This is interpreted as signaling a change in the structure of the amorphous metal itself. In addition there appear to be a small number of other deep-well sites where hydrogen is initially trapped at low concentrations. These have a very broad distribution of activation energies ranging from the main peak down to below 0.1 eV. A model is proposed to account for this by hopping of hydrogen between larger sites through distorted four-sided faces in the metal lattice.
", "doi": "10.7907/t60e-ft46", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:7983", "collection": "thesis", "collection_id": "7983", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10092013-140441093", "primary_object_url": { "basename": "Le Bras_r_1985.pdf", "content": "final", "filesize": 26322234, "license": "other", "mime_type": "application/pdf", "url": "/7983/1/Le Bras_r_1985.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Methods of Multiparameter Inversion of Seismic Data Using the Acoustic and Elastic Born Approximations", "author": [ { "family_name": "Le Bras", "given_name": "Ronan", "orcid": "0000-0003-2439-6938", "clpid": "Le-Bras-Ronan" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Clayton", "given_name": "Robert W.", "orcid": "0000-0003-3323-3508", "clpid": "Clayton-R-W" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This thesis presents two different forms of the Born approximations for acoustic and elastic wavefields and discusses their application to the inversion of seismic data. The Born approximation is valid for small amplitude heterogeneities superimposed over a slowly varying background. The first method is related to frequency-wavenumber migration methods. It is shown to properly recover two independent acoustic parameters within the bandpass of the source time function of the experiment for contrasts of about 5 percent from data generated using an exact theory for flat interfaces. The independent determination of two parameters is shown to depend on the angle coverage of the medium. For surface data, the impedance profile is well recovered.
\r\n\r\nThe second method explored is mathematically similar to iterative tomographic methods recently introduced in the geophysical literature. Its basis is an integral relation between the scattered wavefield and the medium parameters obtained after applying a far-field approximation to the first-order Born approximation. The Davidon-Fletcher-Powell algorithm is used since it converges faster than the steepest descent method. It consists essentially of successive backprojections of the recorded wavefield, with angular and propagation weighing coefficients for density and bulk modulus. After each backprojection, the forward problem is computed and the residual evaluated. Each backprojection is similar to a before-stack Kirchhoff migration and is therefore readily applicable to seismic data. Several examples of reconstruction for simple point scatterer models are performed. Recovery of the amplitudes of the anomalies are improved with successive iterations. Iterations also improve the sharpness of the images.
\r\n\r\nThe elastic Born approximation, with the addition of a far-field approximation is shown to correspond physically to a sum of WKBJ-asymptotic scattered rays. Four types of scattered rays enter in the sum, corresponding to P-P, P-S, S-P and S-S pairs of incident-scattered rays. Incident rays propagate in the background medium, interacting only once with the scatterers. Scattered rays propagate as if in the background medium, with no interaction with the scatterers. An example of P-wave impedance inversion is performed on a VSP data set consisting of three offsets recorded in two wells.
\r\n", "doi": "10.7907/14q2-fa62", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:3777", "collection": "thesis", "collection_id": "3777", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09262002-154053", "primary_object_url": { "basename": "Boslough_mb_1984.pdf", "content": "final", "filesize": 8832552, "license": "other", "mime_type": "application/pdf", "url": "/3777/1/Boslough_mb_1984.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Shock-Wave Properties and High-Pressure Equations of State of Geophysically Important Materials", "author": [ { "family_name": "Boslough", "given_name": "Mark Bruce", "orcid": "0000-0001-6912-4608", "clpid": "Boslough-Mark-Bruce" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Corngold", "given_name": "Noel Robert", "clpid": "Corngold-N-R" }, { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Roshko", "given_name": "Anatol", "clpid": "Roshko-A" }, { "family_name": "Vreeland", "given_name": "Thad", "clpid": "Vreeland-T" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Shock wave (Hugoniot), shock temperature, and release data are presented for several geophysically important, refractory materials. A sensitive multichannel optical pyrometer was developed to measure shock temperatures (2500 to 5600\u00b0K at pressures from 48 to 117 GPa) in anorthite (CaAl2Si2O8) glass. Shock temperatures of 3750 to 6000\u00b0K at pressures from 140 to 182 GPa were measured in calcium oxide (CaO). Temperature data were used to constrain the energetics of the B1-B2 phase transition at 70 GPa in CaO, and to construct a finite-strain equation of state for CaO consistent with previous Hugoniot data.
\r\n\r\nThe new CaO equation of state was used with equation of state parameters of other oxides to construct a theoretical mixed oxide Hugoniot of anorthite, which is in agreement with new Hugoniot data above about 50 GPa, determined using new experimental techniques developed in this study. The mixed oxide model, however, overestimates the shock temperatures, and does not accurately predict measured release paths. Both shock temperature and release data for anorthite indicate that several high pressure phase regions of stability exist above 50 GPa. A similar mixed oxide Hugoniot was constructed for lunar gabbroic anorthosite, and agrees with two new Hugoniot points at 120 GPa. Release data from lunar gabbroic anorthosite shocked to 120 GPa give evidence for shock vaporization.
\r\n\r\nBecause the densities and bulk properties of CaO and the high pressure phase or phases of anorthite are so close to those determined seismologically for the lower mantle, the amount of these materials present in the lower mantle is not well constrained. The possibility of significant enrichment of the lower mantle in these refractory materials, as predicted by inhomogeneous accretion models, is still open.
\r\n\r\nA simple model is developed to explain the measured time dependences of radiated light in the shock temperature experiments, and constrain the absorption coefficient of the shocked material. The absorption coefficient is found to be an increasing function of shock pressure in shocked anorthite glass.
\r\n\r\nHugoniot and release paths were determined using electromagnetic particle velocity gauges for San Gabriel anorthosite and San Marcos Gabbro shocked to peak stresses between 5 and 11 GPa. The data indicate a loss of shear strength in both rocks, and a partial phase transition of the anorthosite to a denser phase. This implies that estimates of shock wave attenuation in these materials based on elastic-plastic models are too high, and previously calculated amounts of internal energy gained by surface materials from impact or explosion events have been underestimated.
", "doi": "10.7907/C9GZ-3121", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:11236", "collection": "thesis", "collection_id": "11236", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10172018-114703911", "primary_object_url": { "basename": "Hofmeister_AM_1984.pdf", "content": "final", "filesize": 138472836, "license": "other", "mime_type": "application/pdf", "url": "/11236/1/Hofmeister_AM_1984.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "A Spectroscopic and Chemical Study of the Coloration of Feldspars by Irradiation and Impurities, Including Water", "author": [ { "family_name": "Hofmeister", "given_name": "Anne Marie", "clpid": "Hofmeister-Anne-Marie" } ], "thesis_advisor": [ { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" } ], "thesis_committee": [ { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-W-B" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Natural smoky color or smoky color induced by ionizing radiation develops only in potassium feldspars (KAlSi3O8) free of water bound in the feldspar structure. Neither fluid inclusion water nor \u2261SiOH have an effect. The optical absorption spectra of the smoky color consist of polarized bands at 11600, 16200, 19100, and 27200 cm-1, whose integrated intensities are linearly correlated with the integrated intensity of a broad, asymmetric first derivative at geff = 2.027 in electron paramagnetic resonance (EPR) spectra. This hole center forms only in KAlSi3O8 without structurally bound H2O, and in microcline is resolved into an asymmetric six-line pattern at geff = 2.024 and a single derivative at geff = 2.009 which are Si-O- -K and a hole shared between two nonbonding oxygens (NBO) on Si. In analogy to coloring in quartz and glass, the 11600 cm-1 band is caused by a hole trapped between two NBO's on silicon, the 16200 and 27200 cm-1 bands are due to the Si-O- -K center, and the 19100 cm-1 band results from a hole trapped on an oxygen attached to two aluminums. Smoky centers do not develop in feldspars with structural water because irradiation mobilizes protons which, while diffusing, destroy centers in their path, and finally then settle in sites similar to their original site. Smoky color also develops in sodic plagioclases, but high Al content inhibits its formation in labradorite.
\r\n\r\nAmazonite color is intrinsic and controlled by an absorption minimum between three overlapping bands in the ultraviolet and a broad band in \u03b2 at 630, or one UV band and a broad band in \u03b2 at 720 nm, or both superimposed. Comparison of EPR to optical integrated intensities shows that all three colors are connected with a first derivative at geff = 1.56 and two satellites of about 1/7 intensity at geff of 1.83 and 1.39. Analysis of the EPR pattern shows that this center is Pb3+ 31% of the time, with the hole located on coordinating oxygens for the remaining 69%. This center is only produced in samples which have in addition to Pb, H2O structurally bound in the lattice. The dependence of color intensity on the smaller molar concentration of structural water or lead implies that lead and structural water in a 1:1 ratio produce color centers in amazonite. The first order reaction kinetics of amazonite color formation by irradiation and the observation that water is not consumed in the process suggests that Pb2+ is oxidized to Pb3+ by the product OH of the irradiation-induced dissociation of water while H concurrently destroys a hole center on an oxygen, and is followed by the regeneration of the water molecule. The kinetics also show that the radiation necessary for the coloration is provided by internal decay of 40K. The two end-member color types (630 or 720 nm) occur for microcline or orthoclase local structure, respectively. Al/Si disorder increases first locally, and then overall as larger amounts Pb or H2O are incorporated, so that crystals with intermediate Pb contents have both color types. A spectrally similar blue radiation color also occurs for Pb-bearing sodic plagioclases.
\r\n\r\nGemmy labradorite phenocrysts from one Steens Mountain basalt flow in Rabbit Basin, Oregon, sometimes possess a pink schiller, or more rarely a transparent red or green coloration. Direct microprobe analysis of the schiller flakes show that these are metallic copper. XRF analysis of the different colored zones revealed that only the copper content varies with color: colorless samples, or sections of crystals, have 0-35 ppm Cu; greens average 80 ppm Cu; reds average 135 ppm Cu; while schiller bearing labradorites have 50 to 240 ppm Cu. Spectral similarity of the red color to copper-ruby color of glass shows that the red arises from the intrinsic absorption of colloidal Cuo particles that are too small to scatter light (ca. 4 to 22 nm). Spectra from the green regions strongly resemble that of amazonite. Because the temperature of exsolution is subsolidus and proportional to Cu content, diffusion proceeds more rapidly for crystals with higher Cu content and results in formation of larger particles. The Cuo reduction at low temperature (800\u00b0C) involves formation of hole center (O-) that is captured by Pb2+ to form the green amazonite color (Pb3+). At high temperatures (~ 900 to 1100\u00b0C) the reduction of Cu is controlled by whatever reactions occur in the basalt to keep fO2 along the QFM buffer. Migration of Cuo may cause the variation of Cu concentrations in a single sample; but the variation of Cu content among different crystals suggests that the composition of the megacrysts was not constant and changed in response to an increasing copper content in the melt as crystallization of the labradorite proceeded.
\r\n\r\nThe coloration process in feldspar strongly resembles that in glasses for both radiation colors (smoky) and exsolution phenomena (Cuo colloids, Cuo schiller) and also that of radiation colors in other crystalline solids (smoky quartz, Pb3+ or Tl2+ in KCl). Although quartz and glass are structurally and chemically similar to feldspar, KCl is not, suggesting that for the most part it is the behavior of the chemical impurity on an atomic level which controls the coloring mechanism.
\r\n", "doi": "10.7907/bj75-5674", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:11316", "collection": "thesis", "collection_id": "11316", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12142018-091056975", "primary_object_url": { "basename": "Shaw_HF_III_1984.pdf", "content": "final", "filesize": 99999823, "license": "other", "mime_type": "application/pdf", "url": "/11316/1/Shaw_HF_III_1984.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Sm-Nd and Rb-Sr Isotopic Systematics of Tektites and Other Impactites, Appalachian Mafic Rocks, and Marine Carbonates and Phosphates", "author": [ { "family_name": "Shaw", "given_name": "Henry Francis, III", "orcid": "0000-0003-0681-5430", "clpid": "Shaw-Henry-Francis-III" } ], "thesis_advisor": [ { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" }, { "family_name": "Wasserburg", "given_name": "Gerald J.", "orcid": "0000-0002-7957-8029", "clpid": "Wasserburg-G-J" }, { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This thesis is made up of three separate studies, each using the Sm-Nd and Rb-Sr isotopic systems to solve a problem of geologic interest.
\r\n\r\nIn the first study it is shown that Sm-Nd and Rb-Sr analyses of tektites and other impactites can be used to place constraints on the age and provenance of the target materials which were impact melted to form these objects. Tektites have large negative values of \u03b5Nd(0) which are uniform within each tektite group, while the \u03b5Sr(0) values are large positive and show considerable variation within each group. The chemical, trace element, and isotopic compositions of tektites are consistent with their production by melting of sediments derived from old continental crust. Each tektite group is characterized by a uniform Nd model age, TNdCHUR, interpreted as the time of formation of the crustal segment which weathered to form the parent sediment for the tektites: (1) ~1.15AE for Australasian tektites; (2) ~1.9AE for Ivory Coast tektites; (3) ~0.9AE for moldavites; (4) ~0.65AE for North American tektites; and (5) ~0.9AE for high-Si irghizites. Sr model ages, TSrUR, are variable within each group, reflecting Rb-Sr fractionation during weathering and sedimentation. In the favorable limit of very high Rb/Sr ratios TSrUR approaches the time of sedimentation of the parent material which melted to form the tektites. Australasian tektites are derived from ~0.25AE sediments, moldavites from ~0.0AE sediments, and Ivory Coast tektites from ~0.95AE sediments. The parent sediments of the other tektite groups have poorly constrained ages. The isotopic data on the moldavites and Ivory Coast tektites are consistent with their derivation from the Ries and Bosumtwi Craters, respectively. Irghizites are isotopically distinct from the Australasian tektites and are probably not related. Sanidine spherules from an iridium-rich Cretaceous-Tertiary boundary clay were heavily overprinted with seawater-derived Sr and Nd during diagenesis. The inferred initial isotopic composition of the sanidine itself is \u03b5Nd(T) = +2 and \u03b5Sr(T) = +5. These results show that the spherules were not derived from old continental crust or meteoritic potassium feldspar. These objects may represent an impact melt of a mixture of basaltic oceanic crust and overlying sediments and are consistent with an oceanic impact at the Cretaceous-Tertiary boundary. The isotopic data are also consistent with an origin by authigenic growth of the spherules from young detrital material.
\r\n\r\nThe second study in this thesis uses the Sm-Nd and Rb-Sr isotopic systematics of mafic rocks from the Appalachians to place constraints on their origin. Isotopic analyses of modern oceanic basalts and ophiolites have shown that both modern and ancient oceanic crust have a characteristic Nd and Sr isotopic signature indicative of derivation from a depleted mantle reservoir. It also appears that the Nd isotopic system is not appreciably disturbed by metamorphism. These isotopic characteristics have been extended to the Pt. Sal, Kings-Kaweah, and Josephine Ophiolites of California. These characteristics are used in an attempt to identify pieces of proto-Atlantic oceanic crust among the mafic and ultramafic rocks of the Appalachians. Sm-Nd mineral isochrons for the Baltimore Mafic Complex, Md (BMC) yield an age of 490\u00b120 My which is interpreted as the igneous crystallization age. BMC whole rock samples do not define isochrones and have initial isotopic compositions of -6.4 < \u03b5Nd(T) < -2.2, +51 < \u03b5Sr(T) < +115. \u03b5Nd(T) and \u03b5Sr(T) are anti-correlated. This is not the signature of depleted mantle and oceanic crust, but is similar to old continental crust. It is proposed that the BMC is a mafic continental intrusion, possibly subduction related, which was contaminated with old continental crust during emplacement. Whole rock samples from the Thetford Mines Complex, Qe (TMC) do not define isochrons and have -1.5 < \u03b5Nd(T) < +4.2, +2.6 < \u03b5Sr(T) < +114. These data do not in any way reflect the signature of normal oceanic crust. These results are in contrast with geologic relationships which show the TMC to have the characteristics of an ophiolite complex. The TMC is chemically and isotopically similar to a class of other ophiolites which have affinities to modern boninites. The TMC may therefore represent an ophiolite formed under an arc complex. The Chunky Gal Amphibolite, N.C., Lake Chatuge complex, N.C., and Hazen's Notch Amphibolite, Vt., were found to have a depleted mantle signature with +5 < \u03b5Nd(T) < +8 and may be fragments of oceanic crust. The Webster-Addie body, N.C., has \u03b5Nd(T) ~-1, \u03b5Sr(T) ~+30 and is not isotopically similar to oceanic crust or the other North Carolina mafic bodies analyzed. From these isotopic results it is clear that Appalachian mafic rocks have diverse origins, some are continental intrusives (BMC), others are probably fragments of oceanic crust (Vermont and N. Carolina amphibolites). Future models for the development of the Appalachians must allow for these various origins. The possibility that some ophiolites are not normal oceanic crust but have an origin in a partially continental setting or as anomalous oceanic crust will require further attention.
\r\n\r\nThe final study is an exploration of the possibility of establishing the Nd isotopic variations in seawater over geologic time by analysing a marine sedimentary phase which records and preserves the \u03b5Nd(T) value of the seawater in which it formed. Apatite and CaCO3 (calcite and aragonite) are examined as possible such phases. Modern biogenic and inorganic calcite and aragonite were found to have low REE concentrations: Nd = 0.2 to 65 ppb. The \u03b5Nd(0) values of Atlantic (-8.3 to -9.6) and Pacific (-0.1 to -1.3) carbonates are distinctly different and reflect the isotopic composition of Nd in the seawater in which they formed. The high concentrations of REE measured in limestones and carbonate fossils cannot be primary but must be due to the presence of other phases in the carbonate of the introduction of REE during diagenesis. Modern biogenic apatite also has a low REE content (<150 ppb Nd), but appears to quickly scavenge REE from seawater. Levels up to 1000 ppm Nd can be reached by this process. Inorganically precipitated apatite from phosphorites also has high concentrations of seawater-derived REE. A seawater-like REE pattern with a characteristic negative Ce-anomaly is often preserved by sedimentary apatite and apatite samples of the same age from different localities bordering a common sea record a common value of \u03b5Nd(T). These characteristics suggest that apatite can be used to trace the evolution of \u03b5Nd(T) in ancient seawater. The values of \u03b5Nd(T) in seawater as inferred from analyses of conodonts and phosphorite apatite range between -1.7 and -8.9 over the last 700My. These values lie in the range of modern seawater values and show no evidence for drastic changes in the sources for Nd in seawater during this time. High values of seawater \u03b5Nd(T) in the Triassic and latest Precambrian may correlate with the breakup of large continental landmasses. The initial \u03b5Nd(T) = -15.0 of the 2AE old Rum Jungle phosphorite requires the presence of -1.5AE old continental crust at 2AE ago. This demonstrates how the \u03b5Nd value of ancient seawater can be used to constrain the age of the exposed crust as a function of time.
", "doi": "10.7907/x0zc-7w22", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:3214", "collection": "thesis", "collection_id": "3214", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08242006-080724", "primary_object_url": { "basename": "echelmeyer-ka_1983.pdf", "content": "final", "filesize": 11189946, "license": "other", "mime_type": "application/pdf", "url": "/3214/12/echelmeyer-ka_1983.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Response of Blue Glacier to a Perturbation in Ice Thickness: Theory and Observation", "author": [ { "family_name": "Echelmeyer", "given_name": "Keith Alan", "clpid": "Echelmeyer-Keith-Alan" } ], "thesis_advisor": [ { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" } ], "thesis_committee": [ { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-W-B" }, { "family_name": "Meier", "given_name": "Mark", "clpid": "Meier-M" }, { "family_name": "Sharp", "given_name": "Robert P.", "clpid": "Sharp-R-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "A unique natural experiment has occurred on Mt. Olympus, Washington, in which the lower part of Blue Glacier has undergone a marked increase in ice thickness and a general decrease in surface slope. In response to this, the glacier flow velocities have increased considerably. The detailed study of the surface configuration and flow of the glacier during the period 1957-59, before the thickening (Meier, et al., 1974) provides a complete baseline against which the recent changes in geometry and surface velocity field are measured.
\r\n\r\nA detailed evaluation of the flow response to the changes in thickness and slope is made, testing for the existence of a quantitative observational relation among u, H, and \u03b1. A linear relation between the percentage ice thickness change and the percentage velocity increase is found. The slope of this response line is related to the exponent n in the flow law of ice, and the negative intercept represents an overall decrease in surface slope.
\r\n\r\nDetailed quantitative interpretations of the field measurements on the flow of Blue Glacier and its response to the change in surface configuration are made, using analytical and finite-element techniques.
\r\n\r\nA theoretical discussion of the effects of longitudinal stress gradients on the flow of an ice mass is given. This discussion leads to the development of an exponential Green's function which determines the effect of surface slope and ice thickness variations on the flow. This Green's function provides a weighting factor for longitudinal averaging of slope and thickness. The characteristic length scale up- and downglacier is dependent on the longitudinal strain-rate, the amount of basal sliding, and the flow-law parameters, being approximately three times the mean ice thickness. Application of this longitudinal averaging to the observed slope and thickness changes results in a marked decrease in deviations of the response data from a linear regression on the velocity changes, showing that longitudinal stress gradients are important.
\r\n\r\nA finite-element computer code for the calculation of flow of ice in channel cross sections of arbitrary shape, including transverse flow components, is developed. The model is applied to flow in channels of idealized parabolic cross-sectional shape to reveal the basic effects of channel shape and flow-law parameters on stress and velocity distribution. The stresses are found to be dependent on the flow-law parameters. Components of transverse flow within the cross section that develop in response to transverse convexity of the glacier surface were calculated. Comparison with observations shows that much of the splaying of the velocity vectors within an ablation zone can be attributed to flow driven by this convex surface.
\r\n\r\nAnalytical models of the flow of a glacier in which the flow law parameters vary with position are developed. These models show that there is a nonuniqueness in flow-law parameters obtained from borehole deformation studies. Studies of the response of a glacier to a change in surface configuration can partially eliminate some of this ambiguity.
\r\n\r\nThe theory and finite element calculations are extended to channels that follow a curving course in map view, which is necessary for application to Blue Glacier, since in the reach studied the glacier flows around a gently curving bend of 90\u00b0. Longitudinal channel curvature causes asymmetry in the stress and velocity distribution within a symmetric channel. The stress centerline is shifted toward the inside of the bend, while the position of the maximum velocity is usually shifted outward of the center for n \u2265 3. The effects of curvature are readily observable in the flow and crevassing of Blue Glacier.
\r\n\r\nThe relation between perturbations in ice thickness and surface slope and the change in velocity is developed for arbitrary channels. Analytical and numerical results indicate that there is a linear relation between the changes in slope \u03b1, thickness H, and surface velocity u:
\r\n\r\n[Equation included in scanned thesis' abstract, pp. vii]
\r\n\r\nwhere \u03a8 is termed the response factor. For realistic channel geometries, \u03a8 is in the range 1/2 to 1. This factor represents the change in cross-sectional shape of an ice mass which accompanies a change in ice thickness within a given channel. The value of the stress exponent inferred from the observed flow response is significantly affected by this geometric factor, which is approximately equal to 0.82 for Blue Glacier. The slope of the response line implies that n = 4 for the flow of Blue Glacier when this response factor is taken into account.
\r\n\r\nFinite element models of flow and the flow response within the different cross sections of Blue Glacier (as determined by radio echo sounding) compare well with the observed velocity patterns and response to change in thickness if channel curvature is included. These results again imply a stress exponent of n = 4. The results also agree with the various field measurements which indicate that basal sliding contributes at most 10% to the overall motion of the glacier.
\r\n\r\nThe results presented in this thesis represent the most detailed evaluation of the response of a glacier to perturbations in ice thickness and surface slope. They show that non-linear flow theory with n = 4 is applicable to a good approximation. The relationship between the flow velocity, slope, and thickness found in this work has direct application to the study of effects of climatic change on an ice mass.
", "doi": "10.7907/ZQHK-NA29", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:7466", "collection": "thesis", "collection_id": "7466", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02062013-144652620", "primary_object_url": { "basename": "Jakosky_bm_1983.pdf", "content": "final", "filesize": 41355084, "license": "other", "mime_type": "application/pdf", "url": "/7466/1/Jakosky_bm_1983.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "The Seasonal Behavior of Water Vapor in the Mars Atmosphere", "author": [ { "family_name": "Jakosky", "given_name": "Bruce Martin", "orcid": "0000-0002-0758-9976", "clpid": "Jakosky-Bruce-Martin" } ], "thesis_advisor": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "thesis_committee": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Farmer", "given_name": "C. Bernard", "clpid": "Farmer-C-Bernard" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Understanding the evolution of volatiles on Mars requires understanding the processes which are currently acting to cause exchange between the various reservoirs on annual and longer timescales. On the seasonal timescale, exchange of water can occur between the atmosphere and reservoirs of ice in the polar caps and of adsorbed water in the near-surface regolith covering the remainder of the planet. This exchange is driven by the seasonally-varying insolation and its consequent effects on the surface and subsurface temperatures and on the advance and retreat of the predominantly-CO2 polar caps. On a longer timescale, exchange can occur between these same reservoirs, and is driven by the changing annual insolation patterns which result from the 105-year timescale variations in Mars' orbital elements (predominantly the orbital obliquity). Observations of the seasonal water cycle and its variations from year to year from the Viking spacecraft and from Earth provide clues as to the importance of the various reservoirs and provide boundary conditions against which models of the various processes can be compared.
\r\n\r\nThe water vapor content of the Mars atmosphere was measured from the Viking Orbiter Mars Atmospheric Water Detectors (MAWD) for a period of more than one Martian year, from June, 1976, through April. 1979, and the results are presented here. The data reduction incorporates spatial and seasonal variations in surface pressure, and supplements earlier published versions of less-complete data. Column abundances vary between zero and about 100 precipitable microns (pr \u00b5m), depending on location and season, while the entire global abundance varies seasonally between an equivalent of about 1 and 2 km3 of ice. The first appearance of vapor at non-polar latitudes as northern summer approaches, and the drop in abundance at mid-latitudes as summer ends, both strongly imply the existence of a seasonal reservoir for water within the regolith. There appear to be no net annual sources away from the poles that contribute significant amounts of water. However, the strong annual gradient of vapor from north to south implies a net annual flow of vapor toward the south; this southward flow may be balanced in part by a northward flow during the global dust storms, by transport in the form of clouds or adsorbed onto dust grains, or during other years. The perennially-cold nature of the south-polar residual cap, along with the relatively large summertime vapor abundances over the cap, implies a net annual condensation of vapor onto the cap. Estimates are made of the southward transport, and are consistent with the movement of ice being important in the formation and evolution of the polar layered terrain, and with the formation of the individual layers at the rate of one per obliquity cycle (105 years).
\r\n\r\nThe global distribution of the annual average abundance of vapor is found to correlate well with Martian topography, as might be expected for a uniform constant atmospheric mixing ratio. If this topographic effect is divided out, the resulting residual map correlates with maps of surface albedo and thermal inertia; this correlation may be related to the control exerted by the surface and subsurface temperatures on the adsorption/desorption process and on the atmospheric temperature profile and, hence, the vapor holding capacity of the atmosphere.
\r\n\r\nThe vertical distribution of vapor within the atmosphere is inferred through comparison of the observed water vapor abundances with measurements of atmospheric temperatures. In order to not saturate, the vapor must be confined to the lowermost 1 to 3 scale heights (~ 10-30 km), with this height varying with location and season. Near-surface water vapor can condense out overnight and form a morning fog; estimates of the optical thickness of the resulting fog are made, and they agree well with observations of diurnal variations of opacity due to fog formation.
\r\n\r\nPrevious Earth-based near-infrared observations are re-interpreted here; they show that water ice condenses out onto the seasonal polar caps, but not during midday near the equator. Earth-based observations of the vapor column abundance are compared with the Viking MAWD results, and indicate that the seasonal cycle shows a remarkable repeatability, except during 1969 when large vapor abundances were present during southern summer. This difference is explained by postulating that all of the CO2 had sublimed off of the south residual cap that year, exposing the underlying water cap which would subsequently sublime and produce large amounts of atmospheric vapor; the rate and amount of CO2 sublimation may depend on the degree of dust storm activity each year and hence on the different thermal loads placed on the cap.
\r\n\r\nThe possible processes for producing seasonal changes in the atmospheric vapor abundances have been modeled in order to infer the relative importance of each process in the seasonal cycle. The equilibrium between water vapor and water adsorbed onto the regolith grains is sufficiently temperature-dependent that seasonal surface temperature variations are capable of driving a large exchange of water between the atmosphere and subsurface. For the likely range of regolith properties, this exchange is found to be from 10-150% of the observed seasonal change in atmospheric abundance; the differences between this exchange and the observed behavior result from transport of vapor due to the atmospheric circulation. Due to the latitudinal gradient of atmospheric vapor, there will also be a gradient of adsorbed water, with the south regolith containing much less water than that in the north; this gradient in the regolith will result independent of the vapor diffusivity in the regolith, as the near-surface water will be able to equilibrate on some timescale.
\r\n\r\nModels have been constructed which include regolith exchange, polar cap formation, and atmospheric transport. Comparison of the model results with the vapor observations and with other data regarding the physical nature of the surface allows constraints to be placed on the relative importance of each process. The models are capable of satisfactorily explaining the gross features of the observed behavior using plausible values for the regolith and atmosphere mixing terms. In the region between the polar caps, the regolith contributes as much water to the seasonal cycle of vapor as does transport in from the more-poleward regions, to within a factor of two. Globally, 10-50% of the seasonal cycle of vapor results from exchange of water with the regolith, about 40% results from the behavior of the residual caps, and the remainder is due to exchange of water with the seasonal caps. It is difficult to determine the relative importance of the processes more precisely than this because both regolith and polar cap exchange of water act in the same direction, producing the largest vapor abundance during the local summer. The system is ultimately regulated on the seasonal timescale by the polar caps, as the time to reach equilibrium between the atmosphere and regolith or between the polar atmosphere and the global atmosphere is much longer than the time for the polar caps to equilibrate with the local atmosphere. This same behavior will bold for longer timescales, with the polar caps being in equilibrium with the insolation as it changes on the obliquity timescale, and the atmosphere and regolith following along.
", "doi": "10.7907/f9fz-gg50", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:11869", "collection": "thesis", "collection_id": "11869", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10282019-161929138", "primary_object_url": { "basename": "Vassiliou_MS_1983.pdf", "content": "final", "filesize": 59116252, "license": "other", "mime_type": "application/pdf", "url": "/11869/1/Vassiliou_MS_1983.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "The Energy Release in Earthquakes, and Subduction Zone Seismicity and Stress in Slabs", "author": [ { "family_name": "Vassiliou", "given_name": "Marios Simou", "clpid": "Vassiliou-Marios-Simou" } ], "thesis_advisor": [ { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" } ], "thesis_committee": [ { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" }, { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Saleeby", "given_name": "Jason B.", "clpid": "Saleeby-J-B" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Part I
\r\n\r\nEarthquake energy calculations are generally made through an empirical application of the familiar Gutenberg-Richter energy-magnitude relationships. The precise physical significance of these relationships is somewhat uncertain. We make use here of the recent increases in knowledge about the earthquake source to place energy measurements on a sounder physical basis. For a simple trapezoidal far-field displacement source-time function with a ratio x of rise time to total duration T0, the seismic energy E is proportional to 1/[x(1-x)2] M20/T30, where M0 is seismic moment. As long as x is greater than 0.1 or so, the effect of rise time is not important. The dynamic energies thus calculated for shallow events are in reasonable agreement with the estimate E \u2248 (5 x 10-5)M0 based on elastostatic considerations. Deep events, despite their possibly different seismological character, yield dynamic energies which are compatible with a static prediction similar to that for shallow events. Studies of strong-motion velocity traces obtained near the sources of the 1971 San Fernando, 1966 Parkfield, and 1979 Imperial Valley earthquakes suggest that even in the distance range of 1-5 km., most of the radiated energy is below 1-2 Hz. in frequency. Far field energy determinations using long period WWSSN instruments are probably not in gross error despite their bandlimited nature. The strong motion record for the intermediate depth Bucharest earthquake of 1977 also suggests little teleseismic energy outside the pass-band of a long period WWSSN instrument.
\r\n\r\nPart II
\r\n\r\nThe pattern of seismicity as a function of depth in the world, and the orientation of stress axes of deep and intermediate earthquakes, are explained using viscous fluid models of subducting slabs, with a barrier in the mantle at 670 km. 670 km is the depth of a seismic discontinuity, and also the depth below which earthquakes do not occur. The barrier in the models can be a viscosity increase of an order of magnitude or more, or a chemical discontinuity where vertical velocity is zero. Log N versus depth, where N is the number of earthquakes, shows (1) a linear decrease to about 250-300 km depth, (2) a minimum near that depth, and (3) an increase thereafter. Stress magnitude in a subducting slab versus depth, for a wide variety of models, shows the same pattern. Since there is some experimental evidence that N is proportional to ek\u03c3, where k is a constant and \u03c3 is the stress magnitude, the agreement is encouraging. In addition, the models predict down-dip compression in the slab at depths below 400 km. This has been observed in earlier studies of earthquake stress axes, and we have confirmed it via a survey of events occurring since 1977 which have been analyzed by moment tensor inversion. At intermediate depths, the models predict an approximate but not precise state of down-dip tension when the slab is dipping. The observations do not show an unambiguous state of down-dip tension at intermediate depths, but in the majority of regions the state of stress is decidedly closer to down-dip tension than it is to down-dip compression. Chemical discontinuities above 670 km, or phase transitions with an elevation of the boundary in the slab, predict, when incorporated into the models, stress peaks which are not mirrored in the profile of seismicity versus depth. Models with an asthenosphere and mesosphere of appropriate viscosity can not only explain the state of stress observed in double Benioff zones, but also yield stress magnitude profiles consistent with observed seismicity. Models where a nonlinear rheology is used are qualitatively consistent with the linear models.
", "doi": "10.7907/yp4p-t246", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:11782", "collection": "thesis", "collection_id": "11782", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08302019-150635775", "type": "thesis", "title": "Holographic In-Situ Stress Measurement in Geophysics", "author": [ { "family_name": "Cohn", "given_name": "Stephen Norfleet", "clpid": "Cohn-Stephen-Norfleet" } ], "thesis_advisor": [ { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-W-B" }, { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "A new and still experimental method for measuring the absolute in-situ stress field in crustal rocks offers several advantages compared to existing in-situ stress measurement techniques. It employs optical holography to record strain-relief displacements in a borehole environment. We call the prototype instrument the holographic stressmeter. It operates in an uncased borehole where it drills strain-relieving side holes into the borehole wall. An interference holographic recording system records the resulting displacements onto film. The reconstructed interference holograms contain sufficient information in their fringe patterns to determine the three-dimensional vector displacements due to strain relief at every point surrounding the side hole. Assuming isotropic, homogeneous, linearly elastic rock, these displacements define the three stresses acting at the borehole wall at a single point. The three non-vanishing stresses acting at each of three points, distributed azimuthally, on the borehole wall provide sufficient constraint to determine all six components of the desired far-field or virgin-rock stress tensor.
\r\n\r\nThe holographic stressmeter employs an on-board side hole drilling system to produce strain relief. Thus it should be economical to operate and it is not restricted to shallow depths as are overcoring techniques. Furthermore, recording the whole displacement field resulting from drilling the side hole reduces the potential contamination of the measurement by residual stress mechanisms which often affect point strain measurements using foil resistance gauges.
\r\n\r\nTo date a complete stress determination in the field has not been attempted. However, a prototype stressmeter has demonstrated repeatedly that the stability necessary to conduct the measurement using this approach is attainable. Results from field deployment show that the stressmeter can make qualitatively correct measurements at one azimuth in a borehole. Modifications to make measurements at the three azimuths required for a complete determination of the stress tensor components should be easily achieved. We propose additional improvements to permit measuring rock elastic properties in situ to enable accurate, quantitative stress determinations. The theoretically predicted precision of the stress component magnitudes using this measurement approach is estimated at 20%.
", "doi": "10.7907/6vsd-wa54", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:1324", "collection": "thesis", "collection_id": "1324", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-04102003-122837", "primary_object_url": { "basename": "gillespie_ar_1982.pdf", "content": "final", "filesize": 50336898, "license": "other", "mime_type": "application/pdf", "url": "/1324/14/gillespie_ar_1982.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Quaternary Glaciation and Tectonism in the Southeastern Sierra Nevada, Inyo County, California", "author": [ { "family_name": "Gillespie", "given_name": "Alan Reed", "clpid": "Gillespie-Alan-Reed" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" }, { "family_name": "Sieh", "given_name": "Kerry E.", "orcid": "0000-0002-7311-2447", "clpid": "Sieh-K-E" }, { "family_name": "Sharp", "given_name": "Robert P.", "clpid": "Sharp-R-P" }, { "family_name": "Wasserburg", "given_name": "Gerald J.", "orcid": "0000-0002-7957-8029", "clpid": "Wasserburg-G-J" }, { "family_name": "Clark", "given_name": "M. M.", "clpid": "Clark-M-M" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The southeastern Sierra Nevada consists of three geographic regions. From west to east, they are: an upland region across the crest, a steep east-facing escarpment along which Owens Valley has partly subsided, and foothill blocks intermediate to the Sierra Nevada and Owens Valley. Farther east, Owens Valley is a deep graben separating the Sierra Nevada and the Inyo Range.
\r\n\r\nThe main goals of this thesis were the detailed mapping of Quaternary glacial and other deposits in these regions, dating of critical events, and geomorphic analysis of the range front. The focus was on Pleistocene moraines near the range front. The motivation of this research was to improve our understanding of the chronology of Pleistocene events, to characterize details of the tectonic history of the Sierra, to infer faulting, erosion, and deposition rates, and to provide a basis for the comparison of the Quaternary geology in the southeastern Sierra and in more intensively studied regions in the central and northern Sierra and elsewhere.
\r\n\r\nThe study area extended from the alluvial fans of Owens Valley west to the Sierra crest from latitude 36\u00b045' N to 37\u00b000' N. It included the southern part of the Big Pine volcanic field, an eruptive center for basaltic lavas for most of the Pleistocene Epoch. Elevations within the study area ranged from about 1000 m (Owens Valley) to about 4000 m (peaks along the crest).
\r\n\r\nThroughout the study area the principal rocks are granodiorite and quartz monzonite of Cretaceous age. Plutons are rather small, and individual drainages generally include more than one. In the southern part of the study area, Jurassic-Triassic metavolcanic rocks are found as roof pendants. These rocks, originally ranging in composition from basalt to rhyolite, are most common near the Sierra crest. In the northern canyons of the study area, Paleozoic metasedimentary rocks including sandy marbles and biotite schist replace the metavolcanic pendants. The foothill blocks are identical to the Sierras in composition.
\r\n\r\nBelow the foothills coalescing alluvial fans grade a few km east to the alluvium and lacustrine sediments of the Owens River and Owens Lake. These sediments have been shown in geophysical studies to mask a second escarpment as high as the one of the range front, and the total bedrock relief from the Sierra crest to the floor of the graben is as much as 6 km.
\r\n\r\nDuring the Quaternary Period the southeastern Sierra Nevada was characterized by the down-faulting of Owens Valley along two zones, one a series of normal faults along the range front (Independence Fault) and the other a series of faults along the center of the valley (Owens Valley fault zone). This same period has seen the cutting of deep canyons through the 2-km-high escarpment. During repeated glaciations these canyons were widened and deepened. Traces of at least seven glaciations were found during this study. Moraines and other deposits left during these glaciations could be distinguished based on the degree of weathering of granitic clasts, vegetative cover, and morphologic characteristics. Absolute age limits were obtained for two of the Pleistocene glaciations by radiometric dating of basalt flows interfingered with the moraines.
\r\n\r\nThree of the recognized glaciations, probably corresponding to the Matthes, Recess Peak, and Hilgard neoglaciations found by J.H. Birman in the central Sierra Nevada, occurred during the Holocene Epoch. The youngest glaciers (Matthes glaciation) left unconsolidated and unvegetated till in stagnant rock glaciers and moraines in cirques on high peaks. Some rock glaciers are still ice-cored. Extending out from the cirques and into the upper reaches of the canyons are moraines correlating to the Recess Peak glaciation. Till is generally consolidated and supports heavy lichen growth and bushes but few trees. The oldest Holocene glaciation (Hilgard) left few large moraines in the study area. Hilgard glaciers extended much farther down-canyon than the younger Holocene glaciers, sometimes within one or two km of the Tioga terminal moraines. Those Hilgard terminal moraines which were found have been barely breached by streams. Moraines tend to be heavily forested, and lakes are largely unsedimented. The Hilgard glaciation may have simply been the last stade of the Tioga glaciation from the evidence found in this study.
\r\n\r\nAt least four Pleistocene glaciations occurred in the southeastern Sierra Nevada. All four postdate most of the significant incision of streams through the escarpment. The three youngest probably correlate with the Tioga, Tenaya, and Tahoe stages (in order of increasing age) recognized throughout the Sierra. In each case, moraine morphology has been well preserved. Tioga moraines were found down to about 2200 m elevation. Nested sets of moraines were common. The terminal moraines of the youngest of these were sometimes intact. lakes were rare; one (Sawmill Meadow) was completely sedimented. Granitic boulders in the moraines were largely unweathered. Weathering of boulders in Tenaya moraines was similar, but a small fraction of granitic boulders were grusy. Boulders from Tahoe moraines were conspicuously weathered, and the moraines themselves were rounded and gullied.
\r\n\r\nThe oldest group of moraines probably significantly predates the Tahoe glaciation. It is nevertheless post-Sherwin. Moraines in this group were found in five of the eight canyons studied. While obviously eroded, these moraines still retained their original shape. All surficial boulders were heavily weathered, but some exposed in road cuts were fresh. No moraines of Sherwin age were identified, although Sherwin till is widespread only a few km to the north. However, on plateaus and ridges 200 to 300 m above the modern canyons near the Sierra crest were found ancient diamictons, some of which could be till. Remnants of U-shaped valleys preserved as high passes across the crest or as cols between canyons east of the crest may be testimonials to ancient glaciers of Sherwin age or older.
\r\n\r\nRadiometric dating (40Ar - 39Ar) of basalts interfingered with moraines in Sawmill Canyon provided a new upper limit of 0.12 my for a moraine of the Tahoe glaciation, and a range of 0.13 - 0.46 my for one pre-Tahoe glaciation. These results confirm that the Tahoe glaciation occurred during the Wisconsin stage of the continental ice age, and conclusively demonstrate the existence of pre-Wisconsin glaciers in the southern Sierra. Relative dating based on acoustic wave speeds through weathered boulders on the moraines indicates the age of the pre-Wisconsin moraine may be close to the upper limit.
\r\n\r\nAlluvial fans appear to have aggraded early in the Wisconsin glaciation (Tahoe glaciation). Subsequently, the fan heads have been incised and the locus of deposition has moved eastward down the fans. The Tenaya and Tioga glaciers during the late Wisconsin stage left outwash plains and terraces along streams cut into the older fans, but aggradation during these events was considerably less than earlier.
\r\n\r\nThree ages of fans were found. The oldest fanglomerate probably is pre-Wisconsin and is exposed in regions protected from later deposition. The heavily weathered fan deposits of this group overlie basalts which appear to be contemporaneous with dated 1.1 - 1.2 my-old basalts nearby. In the middle elevations of the fans, roughly 10 m of fanglomerate was deposited over the old fanglomerate, probably during the Tahoe glaciation. Deposition rates probably are about 0.1 mm/y for the late Pleistocene Epoch. The extent and distribution of the youngest fans (Tenaya-Tioga) are variable, but they are generally found downstream from the incised Tahoe fan heads.
\r\n\r\nFaulting along the range front appears to have been dip-slip only. The offset rate along the range-front faults was determined at several canyons where the fault crossed dated moraines or lava flows. At least during the Wisconsin glaciation faulting on this zone appears to have been erratic, with rates ranging from zero to 0.5 mm/y or more. Offset moraines and terraces at Independence Creek indicated a faulting rate of 0.1 mm/y. Only a few km to the north, Tahoe moraines of both forks of Oak Creek were not offset at all, although scarps could be seen on adjacent hillsides. At Sawmill Creek an offset lava flow gave a lower limit of 0.5 mm/y. It seems that during the late Pleistocene Epoch, offset on the range front faults has been less than on the mid-valley faults east of the study area. Geodetic studies have suggested modern strain rates of 2.2 mm/y for the Owens Valley fault zone.
\r\n\r\nBasalts found in canyons through the escarpment and on terraces and ridges in the foothills to the east document stream erosion during the Pleistocene Epoch. Ridgetop basalts, dated at 1.2 my, stand at least 125 m above the modern streams through the foothills. This indicates an erosion rate of ~ 0.1 mm/y. A comparable rate of ~ 0.15 mm/y for the last 0.46 my was found for Sawmill Creek within the Sierra Nevada. Thus at least during the late Pleistocene Epoch erosion rates in the Sierra and in the foothills have been similar.
\r\n\r\nPatches of boulders and gravels atop the basalt show that some time after 1.2 my BP the foothill block was submerged by alluvial fans. Incision may have begun in response to the inception or renewal of subsidence of the graben along the Owens Valley fault zone.
\r\n\r\nExtensive volcanism in the Big Pine Volcanic field appears to have begun at least 1.2 my ago, and has continued sporadically up to perhaps 0.05 my ago. Minor eruptions may have occurred more recently.
\r\n\r\nThe eastern escarpment of the Sierra Nevada consists of two zones of truncated ridges. Within the study area, the upper zone is about 950 m high; the lower is about 750 m high. Triangular facets of the upper zone have a gradient of only ~ 24\u00b0, lower than slopes of ~ 29\u00b0 in the lower zone. This could be explained if subsidence of Owens Valley along the range-front faults occurred in two great pulses.
\r\n\r\nBoth absolute and relative dating methods were refined for this study. Absolute dating of the K-poor basaltic lavas was done indirectly, by 40Ar - 39Ar analysis of K-rich granitic xenoliths found in the lava. These ancient xenoliths were partially degassed of their accumulated 40Ar during heating in the magma, and it proved possible to date this heating event.
\r\n\r\nIn addition to conventional relative dating methods, a new quantitative approach based on the speed of acoustic waves through individual clasts in a deposit was investigated. This method had been used only once before, on terrace deposits. The technique proved to be very useful, and was capable of discriminating moraines successfully in well-studied canyons in the central Sierra. Acoustic wave speeds may be controlled by the abundance of intergranular cracks in granitic boulders. If this is the case, then this technique relies on different processes than those exploited by conventional methods of relative dating. The successful application to moraines in this study enhances our ability to analyse glacial sequences and complements conventional semi-quantitative methods of relative dating.
", "doi": "10.7907/GNES-QH83", "publication_date": "1982", "thesis_type": "phd", "thesis_year": "1982" }, { "id": "thesis:8766", "collection": "thesis", "collection_id": "8766", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02042015-163349497", "type": "thesis", "title": "Complexity of Rupture Propagation in Large Earthquakes in Relation to Tectonic Environment", "author": [ { "family_name": "Stewart", "given_name": "Gordon Selbie", "clpid": "Stewart-Gordon-Selbie" } ], "thesis_advisor": [ { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" } ], "thesis_committee": [ { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" }, { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" }, { "family_name": "Sieh", "given_name": "Kerry E.", "orcid": "0000-0002-7311-2447", "clpid": "Sieh-K-E" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Complexity in the earthquake rupture process can result from many factors. This study investigates the origin of such complexity by examining several recent, large earthquakes in detail. In each case the local tectonic environment plays an important role in understanding the source of the complexity.
\r\n\r\nSeveral large shallow earthquakes (Ms > 7.0) along the Middle American Trench have similarities and differences between them that may lead to a better understanding of fracture and subduction processes. They are predominantly thrust events consistent with the known subduction of the Cocos plate beneath N. America. Two events occurring along this subduction zone close to triple junctions show considerable complexity. This may be attributable to a more heterogeneous stress environment in these regions and as such has implications for other subduction zone boundaries.
\r\n\r\nAn event which looks complex but is actually rather simple is the 1978 Bermuda earthquake (Ms ~ 6). It is located predominantly in the mantle. Its mechanism is one of pure thrust faulting with a strike N 20\u00b0W and dip 42\u00b0NE. Its apparent complexity is caused by local crustal structure. This is an important event in terms of understanding and estimating seismic hazard on the eastern seaboard of N. America.
\r\n\r\nA study of several large strike-slip continental earthquakes identifies characteristics which are common to them and may be useful in determining what to expect from the next great earthquake on the San Andreas fault. The events are the 1976 Guatemala earthquake on the Motagua fault and two events on the Anatolian fault in Turkey (the 1967, Mudurnu Valley and 1976, E. Turkey events). An attempt to model the complex P-waveforms of these events results in good synthetic fits for the Guatemala and Mudurnu Valley events. However, the E. Turkey event proves to be too complex as it may have associated thrust or normal faulting. Several individual sources occurring at intervals of between 5 and 20 seconds characterize the Guatemala and Mudurnu Valley events. The maximum size of an individual source appears to be bounded at about 5 x 1026 dyne-cm. A detailed source study including directivity is performed on the Guatemala event. The source time history of the Mudurnu Valley event illustrates its significance in modeling strong ground motion in the near field. The complex source time series of the 1967 event produces amplitudes greater by a factor of 2.5 than a uniform model scaled to the same size for a station 20 km from the fault.
\r\n\r\nThree large and important earthquakes demonstrate an important type of complexity --- multiple-fault complexity. The first, the 1976 Philippine earthquake, an oblique thrust event, represents the first seismological evidence for a northeast dipping subduction zone beneath the island of Mindanao. A large event, following the mainshock by 12 hours, occurred outside the aftershock area and apparently resulted from motion on a subsidiary fault since the event had a strike-slip mechanism.
\r\n\r\nAn aftershock of the great 1960 Chilean earthquake on June 6, 1960, proved to be an interesting discovery. It appears to be a large strike-slip event at the main rupture's southern boundary. It most likely occurred on the landward extension of the Chile Rise transform fault, in the subducting plate. The results for this event suggest that a small event triggered a series of slow events; the duration of the whole sequence being longer than 1 hour. This is indeed a \"slow earthquake\".
\r\n\r\nPerhaps one of the most complex of events is the recent Tangshan, China event. It began as a large strike-slip event. Within several seconds of the mainshock it may have triggered thrust faulting to the south of the epicenter. There is no doubt, however, that it triggered a large oblique normal event to the northeast, 15 hours after the mainshock. This event certainly contributed to the great loss of life-sustained as a result of the Tangshan earthquake sequence.
\r\n\r\nWhat has been learned from these studies has been applied to predict what one might expect from the next great earthquake on the San Andreas. The expectation from this study is that such an event would be a large complex event, not unlike, but perhaps larger than, the Guatemala or Mudurnu Valley events. That is to say, it will most likely consist of a series of individual events in sequence. It is also quite possible that the event could trigger associated faulting on neighboring fault systems such as those occurring in the Transverse Ranges. This has important bearing on the earthquake hazard estimation for the region.
", "doi": "10.7907/9d84-pr40", "publication_date": "1982", "thesis_type": "phd", "thesis_year": "1982" }, { "id": "thesis:10832", "collection": "thesis", "collection_id": "10832", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04252018-105910410", "type": "thesis", "title": "Dynamic Properties of Carbonates and Applications to Cratering Processes", "author": [ { "family_name": "Vizgirda", "given_name": "Joana Marija", "clpid": "Vizgirda-Joana-Marija" } ], "thesis_advisor": [ { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" } ], "thesis_committee": [ { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" }, { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The response of carbonate minerals and rocks under shock compression is investigated using equation of state, shock metamorphism, and crater morphology studies. Coralline limestone samples from Cactus Crater, a nuclear explosion crater on Runit Island in Eniwetok Atoll, are used in the investigations of shock deformation as well as the crater structural study. Carbonate minerals and rocks shocked in the laboratory to known dynamic stress levels are used to calibrate shock pressures in the Cactus samples.
\r\n\r\nVery low shock pressure deformation effects are detected in the explosively and laboratory shocked samples by two bulk sample techniques: electron spin resonance (ESR) and powder X-ray diffraction. According to ESR studies on calcite from Cactus Crater samples, peak shock pressures of 4.5\u00b10.5 GPa were experienced by the material beneath the crater. Aragonite peak broadening analyses of powder X-ray diffraction spectra allows differentiation between two modes of material deformation, mosaicism (or reduction of crystallite size) and strain; both of these effects are detected in Cactus and in laboratory shocked samples. According to the X-ray analysis, peak pressures of 3\u00b11.5 GPa were experienced by the Cactus samples. A phase transition model, based on the variation of mosaicism and strain effects with shock pressure, is proposed. According to this model, residual strain in aragonite increases (crystallite size remaining approximately the same) until a threshold pressure of 8 to 10 GPa, corresponding to a phase transition, is reached; release from shock states above this pressure results in a discontinuous decrease in crystallite size and strain.
\r\n\r\nThe diagenetic high to low magnesium calcite transition boundary occurring in the immediate subsurface of Runit Island is used as a stratigraphic tracer to determine structural features beneath Cactus Crater, including the amount of permanent downward displacement, the presence of a 10 m thick breccia lens which is disturbed and extensively mixed in-situ, and a possible central uplift feature. Applying the Bingham plastic model to Cactus Crater gives a yield strength of approximately 1 bar for the shock-wave engulfed limestone rock; this value is similar to the yield strength of many clays, and suggests a partially liquefied state for the water-saturated limestone immediately after passage of the shock wave.
\r\n\r\nThe first aragonite Hugoniot equation of state data are presented. A Hugoniot elastic limit at 2.5\u00b10.8 GPa and a phase transition at 6.5\u00b11.5 GPa are observed. Above 10 GPa, the aragonite and calcite Hugoniots are approximately coincident, suggesting the transformation of both CaCO3 polymorphs to the same high pressure phase. Release adiabats centered at shock pressures above 18 GPa yield pressure-density isentropes which suggest possible dissociation, i.e. CO2 release, during the decompression process. These experimental data disagree with theoretical calculations, which predict incipient vaporization upon release from shock pressures of 55 and 33 GPa on the aragonite and calcite Hugoniots, respectively. Results from release adiabat experiments on calcite agree with the aragonite data and suggest vaporization upon unloading from shock pressures of approximately 37 GPa; a mass balance calculation using the experimental calcite release paths indicates that 45% of the CaCO3 has dissociated upon release to 0.2 GPa pressures.
\r\n\r\n", "doi": "10.7907/dat3-9s72", "publication_date": "1982", "thesis_type": "phd", "thesis_year": "1982" }, { "id": "thesis:7482", "collection": "thesis", "collection_id": "7482", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02152013-145142740", "type": "thesis", "title": "Viscosity Structure of the Lithospheres of Ganymede, Callisto, and Enceladus, and of the Earth's Upper Mantle", "author": [ { "family_name": "Passey", "given_name": "Quinn R.", "clpid": "Passey-Quinn-R" } ], "thesis_advisor": [ { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" }, { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" }, { "family_name": "Shoemaker", "given_name": "Eugene Merle", "clpid": "Shoemaker-E-M" }, { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Craterform and related features on Ganymede and Callisto include bowl-shaped craters, craters with nearly fiat floors, craters with central peaks, craters with central pits, basins, crater palimpsests and penepalimpsests, and giant multiring systems of ridges and furrows. The large majority of all craters larger than 20 km diameter have a central pit. The pits are interpreted as formed by prompt collapse of transient central peaks. Most craters, in all size ranges, are highly flattened as a consequence of topographic relaxation by slow viscous or plastic flow.
\r\n\r\nAnalysis of the global distribution of craters and multiring structures on Callisto reveal that the large multiring structures are concentrated in the leading hemisphere, whereas craters are depleted here. Calculations of model crater retention ages based on a sample of 2000 craters \u2265 30 km in diameter show that the mean age of Callisto's surface is between 4.0 and 4.2 Gy. Variations in the surface ages, derived from different diameter craters, suggests that larger craters are not retained from as early a period in time as were the smaller craters; this is in agreement with the results predicted by viscous relaxation theory where large wavelength features relax at a faster rate than do small wavelength features. Most of the variations in the observed distribution of craters can be explained satisfactorily by the effects due to the formation of multiring structures, and on the viscous relaxation of craters beneath an insulating regolith.
\r\n\r\nAbout 1000 topographic profiles of craters on Ganymede and Callisto were obtained by photoclinometry. Fresh craters on Ganymede and Callisto have depth-to-diameter ratios and rim height-to-diameter ratios similar to those of fresh lunar craters, but most craters are much shallower. Small craters have not flattened or relaxed as much as have large craters; comparison of the crater profiles with the results from theoretical of crater relaxation studies in a viscous medium, allows determination of the viscosity at the surfaces of Ganymede and Callisto, and, also, determination of the viscosity gradient with depth. The derived mean surface viscosity for the lithospheres of Ganymede and Callisto is 1.0 \u00b1 0.5 x 1026 poise. For Ganymede, the estimated thermal gradient at ~3.9 Gya was \u2265 8 K/km; the thermal gradient can be modelled as decreasing approximately exponentially with time, with an e-folding time of about 108 years; the estimated present thermal gradient is \u2264 2.0 K/km. For Callisto, the thermal gradient was \u2265 3 K/km at ~4.1 GYA and the decrease in the thermal gradient can be modelled as an exponential dropoff with an e-folding time between about 5 x 107 and 2 x 108 years; the estimated present thermal gradient on Callisto \u2264 1.5 K/km.
\r\n\r\nHigh resolution Voyager II images of Enceladus reveal that some regions on its surface are highly cratered; the most heavily cratered surfaces probably date back into a period of heavy bombardment. The forms of many of the craters, on Enceladus, are similar to those of fresh lunar craters, but many of the craters are much shallower in depth, and the floors of some craters are bowed up. Analysis of the forms of the flattened craters on Enceladus suggests that the viscosity at the top of the lithosphere, in the most heavily cratered regions, is between 1024 and 1025 poise. The exact time scale for the collapse of the craters is not known, but probably was between 100 My and 4 Gy. The flattened craters are located in regions in which the heat flow was (or is) higher than in the adjacent terrains. Because the temperature at the top of the lithosphere of Enceladus would be less than, or equal to that of Ganymede and Callisto, if it is covered by a thick regolith, and because the required viscosity, on Enceladus, is one to two orders of magnitude less than for Ganymede and Callisto, it can be concluded that the lithospheric material, on Enceladus, is different from that of Ganymede and Callisto. Enceladus possibly has a mixture of ammonia ice and water ice in the lithosphere, whereas the lithospheres of Ganymede and Callisto are composed primarily of water ice.
\r\n\r\nNew field measurements of elevation of Provo-level and Bonneville-level shoreline terraces, of Lake Bonneville, provide data for reanalysis of isostatic rebound in the Lake Bonneviile basin. Analysis of the differential rebound between the Provo shoreline (maximum rebound of 43 m) and the Bonneville shoreline (maximum rebound of 69 m) requires that the latter be an equilibrium shoreline. From the new data, the best estimate of the upper limit of effective viscosity of the uppermost mantle, assuming a half-space model and a 2000 year time interval between the Bonneville and Provo shorelines, is 2 x 1019 N sec m-2 (2 x 1020 poise). In addition, comparison of shoreline rebound profiles, for both shorelines, with theoretical plate flexure models indicates that the mean flexural rigidity of the Basin and Range lithosphere in this region is 1 x 1023 N m, or slightly less.
\r\n\r\n\r\n\r\n", "doi": "10.7907/A31H-FJ81", "publication_date": "1982", "thesis_type": "phd", "thesis_year": "1982" }, { "id": "thesis:3552", "collection": "thesis", "collection_id": "3552", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09152006-102853", "type": "thesis", "title": "Seismic Source Processes and Tectonics: Observations of Four Intracontinental Earthquakes", "author": [ { "family_name": "Cipar", "given_name": "John Joseph", "clpid": "Cipar-John-Joseph" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Harkrider", "given_name": "David G.", "clpid": "Harkrider-D-G" }, { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" }, { "family_name": "Sieh", "given_name": "Kerry E.", "orcid": "0000-0002-7311-2447", "clpid": "Sieh-K-E" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This thesis presents studies of the source processes of four shallow earthquakes and their relation to regional tectonics. In the first chapter, long-period teleseismic P and S waves from the Haicheng, China earthquake of February 4, 1975 are compared directly to time domain synthetic seismograms to infer source parameters. The P-wave focal mechanism indicates that faulting was dominantly left-lateral strike-slip along a northwest striking nodal plane (strike = 288\u00b0, dip = 78\u00b0N, rake = 342\u00b0). The strike of this nodal plane agrees with the trend of the aftershock distribution. Azimuthal variation of P-wave duration is attributed to fault rupture 22 km in a northwesterly direction, along strike of the aftershock zone. There is considerable discrepancy between the observed SH waves and synthetics computed using this model. These discrepancies are due to either structural complexities in the source region or change in fault mechanism as the rupture propagated along strike. Seismic moment, average dislocation and stress drop are computed to be 2.7 x 1026 dyne-cm, 2.5 meters and 48 bars, respectively.
\r\n\r\nThe remaining three chapters present a detailed examination of seismograms recorded by the 1976 Friuli, Italy earthquake (May 6, 1976, MS = 6.5) and two major aftershocks (both on September 15, 1976 at 03h 15m, MS = 6.0 and 09h 21m, MS = 5.9). Teleseismic long-period body waves and surface waves radiated by the mainshock and 09h 21m aftershock are studied in Chapter Two to determine source characteristics. Focal mechanisms along with geological evidence suggest that both events represent underthrusting of the Friuli Plain beneath the Southern Alps. The depths of both earthquakes, estimated by matching synthetic body wave seismograms to observations, are found to lie between 6 and 10 km. Synthetic seismogram calculations which include source directivity effects suggest that the fault length of the mainshock is approximately 16 to 24 km assuming a rupture velocity of 3.0 km/sec. Observations of 100 sec Rayleigh waves confirm the body wave focal mechanism, but suggest that the seismic moment of the mainshock is 5 x 1025 dyne-cm compared to 2.9 x 1025 dyne-cm estimated from body waves. The P-wave moment of the aftershock is 1 x 1025 dyne-cm.
\r\n\r\nIn Chapter Three, short-period records are modeled to obtain additional details of the source time history. Two point sources of radiation are required to adequately model the aftershock short-period records. For the 09h 21m aftershock, the model derived from short-period records also produces good fits to the long-period data. The SP model for the 03h 15m aftershock, on the other hand, predicts long-period synthetics which do not agree with the observations. In particular, the SP moment (0.37 x 1025 dyne-cm) is about 2-1/2 times smaller than the LP moment (1 x 1025 dyne-cm). Adding a long-period component to the SP model considerably improves LP waveform and moment agreement. In the case of the mainshock, a reasonable fit to the observed SP data is obtained using three point sources of radiation. However, LP synthetics computed using this model do not agree with the observations, and the SP moment (0.65 x 1025 dyne-cm) is a small fraction of the LP moment (3-5 x 1025 dyne-cm). Time function durations indicate that the individual events inferred from the SP records are radiated from patches of the fault having radii of 2 to 4 km and stress drops in the range 35 to 276 bars. In comparison, overall stress drops estimated from LP data are found to be 12 bars (mainshock) and 24 bars (09h 21m aftershock). Strong-motion accelerograms are used to put additional constraint on the source geometry of the 09h 21m aftershock.
\r\n\r\nThe 03h 15m and 09h 21m aftershocks are the culminating events of a series of large aftershocks which began on September 11, 1976. Cumulative seismic moment of the Friuli aftershock sequence was as large as the moment released by the mainshock. By comparison, aftershock moments of California earthquakes are typically 1 to 10 percent of the mainshock moment. The large size, location and focal mechanism of the aftershocks suggest that they represent failure of major stress concentrations remaining after the mainshock.
", "doi": "10.7907/bwpb-4c04", "publication_date": "1981", "thesis_type": "phd", "thesis_year": "1981" }, { "id": "thesis:8100", "collection": "thesis", "collection_id": "8100", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02272014-085454874", "primary_object_url": { "basename": "Joesten-rl-1974.pdf", "content": "final", "filesize": 76432892, "license": "other", "mime_type": "application/pdf", "url": "/8100/1/Joesten-rl-1974.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Metasomatism and Magmatic Assimilation at a Gabbro-Limestone Contact, Christmas Mountains, Big Bend Region, Texas", "author": [ { "family_name": "Joesten", "given_name": "Raymond Leonard", "clpid": "Joesten-Raymond-Leonard" } ], "thesis_advisor": [ { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" } ], "thesis_committee": [ { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" }, { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "A composite stock of alkaline gabbro and syenite is intrusive into limestone of the Del Carmen, Sue Peake and Santa Elena Formations at the northwest end of the Christmas Mountains. There is abundant evidence of solution of wallrock by magma but nowhere are gabbro and limestone in direct contact. The sequence of lithologies developed across the intrusive contact and across xenoliths is gabbro, pyroxenite, calc-silicate skarn, marble. Pyroxenite is made up of euhedral crystals of titanaugite and sphene in a leucocratic matrix of nepheline, Wollastonite and alkali feldspar. The uneven modal distribution of phases in pyroxenite and the occurrence' of nepheline syenite dikes, intrusive into pyroxenite and skarn, suggest that pyroxenite represents an accumulation of clinopyroxene \"cemented\" together by late-solidifying residual magma of nepheline syenite composition. Assimilation of limestone by gabbroic magma involves reactions between calcite and magma and/or crystals in equilibrium with magma and crystallization of phases in which the magma is saturated, to supply energy for the solution reaction. Gabbroic magma was saturated with plagioclase and clinopyroxene at the time of emplacement. The textural and mineralogic features of pyroxenite can be produced by the reaction 2( 1-X) CALCITE + ANXABl-X = (1-X) NEPHELINE+ 2(1-X) WOLLASTONITE+ X ANORTHITE+ 2(1-X) CO2. Plagioclase in pyroxenite has corroded margins and is rimmed by nepheline, suggestive of resorption by magma. Anorthite and wollastonite enter solid solution in titanaugite. For each mole of calcite dissolved, approximately one mole of clinopyroxene was crystallized. Thus the amount of limestone that may be assimilated is limited by the concentration of potential clinopyroxene in the magma. Wollastonite appears as a phase when magma has been depleted in iron and magnesium by crystallization of titanaugite. The predominance of mafic and ultramafic compositions among contaminated rocks and their restriction to a narrow zone along the intrusive contact provides little evidence for the generation of a significant volume of desilicated magma as a result of limestone assimilation.
\r\n\r\nWithin 60 m of the intrusive contact with the gabbro, nodular chert in the Santa Elena Limestone reacted with the enveloping marble to form spherical nodules of high-temperature calc-silicate minerals. The phases wollastonite, rankinite, spurrite, tilleyite and calcite, form a series of sharply-bounded, concentric monomineralic and two-phase shells which record a step-wise decrease in silica content from the core of a nodule to its rim. Mineral zones in the nodules vary 'with distance from the gabbro as follows:
\r\n0-5 m CALCITE + SPURRITE + RANKINITE + WOLLASTONITE
\r\n5-16 m CALCITE + TILLEYITE \u00b1 SPURRITE + RANKINITE + WOLLASTONITE
\r\n16-31 m CALCITE + TILLEYITE + WOLLASTONITE
\r\n31-60 m CALCITE + WOLLASTONITE
\r\n60-plus CALCITE + QUARTZ
\r\n\r\nThe mineral of a one-phase zone is compatible with the phases bounding it on either side but these phases are incompatible in the same volume of P-T-XCO2.
Growth of a monomineralio zone is initiated by reaction between minerals of adjacent one-phase zones which become unstable with rising temperature to form a thin layer of a new single phase that separates the reactants and is compatible with both of them. Because the mineral of the new zone is in equilibrium with the phases at both of its contacts, gradients in the chemical potentials of the exchangeable components are established across it. Although zone boundaries mark discontinuities in the gradients of bulk composition, two-phase equilibria at the contacts demonstrate that the chemical potentials are continuous. Hence, Ca, Si and CO2 were redistributed in the growing nodule by diffusion. A monomineralic zone grows at the expense of an adjacent zone by reaction between diffusing components and the mineral of the adjacent zone. Equilibria between two phases at zone boundaries buffers the chemical potentials of the diffusing species. Thus, within a monomineralic zone, the chemical potentials of the diffusing components are controlled external to the local assemblage by the two-phase equilibria at the zone boundaries.
\r\n\r\nMineralogically zoned calc-silicate skarn occurs as a narrow band that separates pyroxenite and marble along the intrusive contact and forms a rim on marble xenoliths in gabbro. Skarn consists of melilite or idocrase pseudomorphs of melili te, one or two . stoichiometric calcsilicate phases and accessory Ti-Zr garnet, perovskite and magnetite. The sequence of mineral zones from pyroxenite to marble, defined by a characteristic calc-silicate, is wollastonite, rankinite, spurrite, calcite. Mineral assemblages of adjacent skarn zones are compatible and the set of zones in a skarn band defines a facies type, indicating that the different mineral assemblages represent different bulk compositions recrystallized under identical conditions. The number of phases in each zone is less than the number that might be expected to result from metamorphism of a general bulk composition under conditions of equilibrium, trivariant in P, T and uCO2. The \"special\" bulk composition of each zone is controlled by reaction between phases of the zones bounding it on either side. The continuity of the gradients of composition of melilite and garnet solid solutions across the skarn is consistent with the local equilibrium hypothesis and verifies that diffusion was the mechanism of mass transport. The formula proportions of Ti and Zr in garnet from skarn vary antithetically with that of Si Which systematically decreases from pyroxenite to marble. The chemical potential of Si in each skarn zone was controlled by the coexisting stoichiometric calc-silicate phases in the assemblage. Thus the formula proportion of Si in garnet is a direct measure of the chemical potential of Si from point to point in skarn. Reaction between gabbroic magma saturated with plagioclase and clinopyroxene produced nepheline pyroxenite and melilite-wollastonite skarn. The calcsilicate zones result from reaction between calcite and wollastonite to form spurrite and rankinite.
\r\n\r\n", "publication_date": "1974", "thesis_type": "phd", "thesis_year": "1974" }, { "id": "thesis:14017", "collection": "thesis", "collection_id": "14017", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12072020-234014838", "primary_object_url": { "basename": "Lagus_PL_1974.pdf", "content": "final", "filesize": 30518048, "license": "other", "mime_type": "application/pdf", "url": "/14017/1/Lagus_PL_1974.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "The Equations of State of Hydrogen and Argon: Applications to the Jovian Interior", "author": [ { "family_name": "Lagus", "given_name": "Peter Leonard", "clpid": "Lagus-Peter-Leonard" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "thesis_committee": [ { "family_name": "Archambeau", "given_name": "Charles B.", "clpid": "Archambeau-C-B" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Hugoniot data for solid argon (initially at 77\u00b0K and l bar) and solid hydrogen (initially at 5\u00b0K and 1 bar) have been obtained to 143 kbar and 6.4 kbar respectively utilizing a propellant gun. The argon data (at volumes of 15.28, 14.84 and 14.64 cc/mole) are in fair agreement with previous shock data, and in excellent agreement with recent theoretically predicted Hugoniots. The hydrogen data (at volumes of 17.10, 15.32, 15.27, 15.11 cc/mole) are compared with Hugoniots calculated from published isothermal compression data. For both argon and hydrogen, the present data are consistent with the assumption that \u03b3/V is constant. Furthermore, to compressions of V/V\u2080 \u2243 0.65, no gross inconsistencies exist between shock-wave and isothermal compression measurements in solid hydrogen.
\r\n\r\nA simple equation of state (E0S) for molecular hydrogen based on a spherically averaged De Boer-type repulsion potential which explicitly includes the zero point energy reproduces experimental pressure-volume data between 5 kbar and 370 kbar. This molecular equa\u00adtion of state when combined with recent metallic equations of state implies a molecular to metallic phase transition pressure of 1.9 \u00b1 0.4 Mbar at 0\u00b0K.
\r\n\r\nA thermally expanded model of Jupiter which incorporates this molecular equation of state, recent metallic hydrogen and helium equa\u00adtions of state, and a van der Waals-type atmosphere yields a model with a hydrogen abundance of x = 0.57. However, the interior temperatures are everywhere above the melting temperature of metallic hydrogen.
", "doi": "10.7907/zzpq-2876", "publication_date": "1974", "thesis_type": "phd", "thesis_year": "1974" } ]